diff --git a/internal/ast/ast.go b/internal/ast/ast.go
index 1a1db67532..04df5e445d 100644
--- a/internal/ast/ast.go
+++ b/internal/ast/ast.go
@@ -10049,6 +10049,7 @@ type SourceFile struct {
 	// Fields set by parser
 	diagnostics                 []*Diagnostic
 	jsdocDiagnostics            []*Diagnostic
+	jsSyntacticDiagnostics      []*Diagnostic
 	LanguageVariant             core.LanguageVariant
 	ScriptKind                  core.ScriptKind
 	IsDeclarationFile           bool
@@ -10147,6 +10148,14 @@ func (node *SourceFile) SetJSDocDiagnostics(diags []*Diagnostic) {
 	node.jsdocDiagnostics = diags
 }
 
+func (node *SourceFile) JSSyntacticDiagnostics() []*Diagnostic {
+	return node.jsSyntacticDiagnostics
+}
+
+func (node *SourceFile) SetJSSyntacticDiagnostics(diags []*Diagnostic) {
+	node.jsSyntacticDiagnostics = diags
+}
+
 func (node *SourceFile) JSDocCache() map[*Node][]*Node {
 	return node.jsdocCache
 }
diff --git a/internal/binder/binder.go b/internal/binder/binder.go
index 05f8bc6382..8e15ad94f3 100644
--- a/internal/binder/binder.go
+++ b/internal/binder/binder.go
@@ -2758,7 +2758,7 @@ func (b *Binder) errorOrSuggestionOnRange(isError bool, startNode *ast.Node, end
 // If so, the node _must_ be in the current file (as that's the only way anything could have traversed to it to yield it as the error node)
 // This version of `createDiagnosticForNode` uses the binder's context to account for this, and always yields correct diagnostics even in these situations.
 func (b *Binder) createDiagnosticForNode(node *ast.Node, message *diagnostics.Message, args ...any) *ast.Diagnostic {
-	return ast.NewDiagnostic(b.file, GetErrorRangeForNode(b.file, node), message, args...)
+	return ast.NewDiagnostic(b.file, scanner.GetErrorRangeForNode(b.file, node), message, args...)
 }
 
 func (b *Binder) addDiagnostic(diagnostic *ast.Diagnostic) {
@@ -2855,83 +2855,3 @@ func isAssignmentDeclaration(decl *ast.Node) bool {
 func isEffectiveModuleDeclaration(node *ast.Node) bool {
 	return ast.IsModuleDeclaration(node) || ast.IsIdentifier(node)
 }
-
-func getErrorRangeForArrowFunction(sourceFile *ast.SourceFile, node *ast.Node) core.TextRange {
-	pos := scanner.SkipTrivia(sourceFile.Text(), node.Pos())
-	body := node.AsArrowFunction().Body
-	if body != nil && body.Kind == ast.KindBlock {
-		startLine, _ := scanner.GetLineAndCharacterOfPosition(sourceFile, body.Pos())
-		endLine, _ := scanner.GetLineAndCharacterOfPosition(sourceFile, body.End())
-		if startLine < endLine {
-			// The arrow function spans multiple lines,
-			// make the error span be the first line, inclusive.
-			return core.NewTextRange(pos, scanner.GetEndLinePosition(sourceFile, startLine))
-		}
-	}
-	return core.NewTextRange(pos, node.End())
-}
-
-func GetErrorRangeForNode(sourceFile *ast.SourceFile, node *ast.Node) core.TextRange {
-	errorNode := node
-	switch node.Kind {
-	case ast.KindSourceFile:
-		pos := scanner.SkipTrivia(sourceFile.Text(), 0)
-		if pos == len(sourceFile.Text()) {
-			return core.NewTextRange(0, 0)
-		}
-		return scanner.GetRangeOfTokenAtPosition(sourceFile, pos)
-	// This list is a work in progress. Add missing node kinds to improve their error spans
-	case ast.KindFunctionDeclaration, ast.KindMethodDeclaration:
-		if node.Flags&ast.NodeFlagsReparsed != 0 {
-			errorNode = node
-			break
-		}
-		fallthrough
-	case ast.KindVariableDeclaration, ast.KindBindingElement, ast.KindClassDeclaration, ast.KindClassExpression, ast.KindInterfaceDeclaration,
-		ast.KindModuleDeclaration, ast.KindEnumDeclaration, ast.KindEnumMember, ast.KindFunctionExpression,
-		ast.KindGetAccessor, ast.KindSetAccessor, ast.KindTypeAliasDeclaration, ast.KindJSTypeAliasDeclaration, ast.KindPropertyDeclaration,
-		ast.KindPropertySignature, ast.KindNamespaceImport:
-		errorNode = ast.GetNameOfDeclaration(node)
-	case ast.KindArrowFunction:
-		return getErrorRangeForArrowFunction(sourceFile, node)
-	case ast.KindCaseClause, ast.KindDefaultClause:
-		start := scanner.SkipTrivia(sourceFile.Text(), node.Pos())
-		end := node.End()
-		statements := node.AsCaseOrDefaultClause().Statements.Nodes
-		if len(statements) != 0 {
-			end = statements[0].Pos()
-		}
-		return core.NewTextRange(start, end)
-	case ast.KindReturnStatement, ast.KindYieldExpression:
-		pos := scanner.SkipTrivia(sourceFile.Text(), node.Pos())
-		return scanner.GetRangeOfTokenAtPosition(sourceFile, pos)
-	case ast.KindSatisfiesExpression:
-		pos := scanner.SkipTrivia(sourceFile.Text(), node.AsSatisfiesExpression().Expression.End())
-		return scanner.GetRangeOfTokenAtPosition(sourceFile, pos)
-	case ast.KindConstructor:
-		if node.Flags&ast.NodeFlagsReparsed != 0 {
-			errorNode = node
-			break
-		}
-		scanner := scanner.GetScannerForSourceFile(sourceFile, node.Pos())
-		start := scanner.TokenStart()
-		for scanner.Token() != ast.KindConstructorKeyword && scanner.Token() != ast.KindStringLiteral && scanner.Token() != ast.KindEndOfFile {
-			scanner.Scan()
-		}
-		return core.NewTextRange(start, scanner.TokenEnd())
-		// !!!
-		// case KindJSDocSatisfiesTag:
-		// 	pos := scanner.SkipTrivia(sourceFile.Text(), node.tagName.pos)
-		// 	return scanner.GetRangeOfTokenAtPosition(sourceFile, pos)
-	}
-	if errorNode == nil {
-		// If we don't have a better node, then just set the error on the first token of
-		// construct.
-		return scanner.GetRangeOfTokenAtPosition(sourceFile, node.Pos())
-	}
-	pos := errorNode.Pos()
-	if !ast.NodeIsMissing(errorNode) && !ast.IsJsxText(errorNode) {
-		pos = scanner.SkipTrivia(sourceFile.Text(), pos)
-	}
-	return core.NewTextRange(pos, errorNode.End())
-}
diff --git a/internal/checker/utilities.go b/internal/checker/utilities.go
index 321d069819..fab2c52440 100644
--- a/internal/checker/utilities.go
+++ b/internal/checker/utilities.go
@@ -23,7 +23,7 @@ func NewDiagnosticForNode(node *ast.Node, message *diagnostics.Message, args ...
 	var loc core.TextRange
 	if node != nil {
 		file = ast.GetSourceFileOfNode(node)
-		loc = binder.GetErrorRangeForNode(file, node)
+		loc = scanner.GetErrorRangeForNode(file, node)
 	}
 	return ast.NewDiagnostic(file, loc, message, args...)
 }
diff --git a/internal/compiler/program.go b/internal/compiler/program.go
index 1786078277..172ff45943 100644
--- a/internal/compiler/program.go
+++ b/internal/compiler/program.go
@@ -865,6 +865,11 @@ func (p *Program) getOptionsDiagnosticsOfConfigFile() []*ast.Diagnostic {
 }
 
 func (p *Program) getSyntacticDiagnosticsForFile(ctx context.Context, sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	// For JavaScript files, we report semantic errors for using TypeScript-only
+	// constructs from within a JavaScript file as syntactic errors.
+	if jsSyntacticDiagnostics := sourceFile.JSSyntacticDiagnostics(); len(jsSyntacticDiagnostics) > 0 {
+		return slices.Concat(jsSyntacticDiagnostics, sourceFile.Diagnostics())
+	}
 	return sourceFile.Diagnostics()
 }
 
diff --git a/internal/parser/js_diagnostics.go b/internal/parser/js_diagnostics.go
new file mode 100644
index 0000000000..41acb70b20
--- /dev/null
+++ b/internal/parser/js_diagnostics.go
@@ -0,0 +1,522 @@
+package parser
+
+import (
+	"github.com/microsoft/typescript-go/internal/ast"
+	"github.com/microsoft/typescript-go/internal/core"
+	"github.com/microsoft/typescript-go/internal/diagnostics"
+	"github.com/microsoft/typescript-go/internal/scanner"
+)
+
+// jsDiagnosticsVisitor is used to find TypeScript-only constructs in JavaScript files
+type jsDiagnosticsVisitor struct {
+	sourceFile               *ast.SourceFile
+	diagnostics              []*ast.Diagnostic
+	walkNodeForJSDiagnostics func(node *ast.Node) bool
+}
+
+// getJSSyntacticDiagnosticsForFile returns diagnostics for TypeScript-only constructs in JavaScript files
+func getJSSyntacticDiagnosticsForFile(sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	visitor := &jsDiagnosticsVisitor{
+		sourceFile: sourceFile,
+	}
+	visitor.walkNodeForJSDiagnostics = visitor.walkNodeForJSDiagnosticsWorker
+
+	// Walk the entire AST to find TypeScript-only constructs
+	sourceFile.ForEachChild(visitor.walkNodeForJSDiagnostics)
+
+	return visitor.diagnostics
+}
+
+// walkNodeForJSDiagnostics walks the AST and collects diagnostics for TypeScript-only constructs
+func (v *jsDiagnosticsVisitor) walkNodeForJSDiagnosticsWorker(node *ast.Node) bool {
+	if node == nil {
+		return false
+	}
+
+	parent := node.Parent
+
+	// Bail out early if this node has NodeFlagsReparsed, as they are synthesized type annotations
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return false
+	}
+
+	// Handle specific parent-child relationships first
+	switch parent.Kind {
+	case ast.KindParameter, ast.KindPropertyDeclaration, ast.KindMethodDeclaration:
+		// Check for question token (optional markers)
+		if parent.Kind == ast.KindParameter && parent.AsParameterDeclaration() != nil && parent.AsParameterDeclaration().QuestionToken == node {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, scanner.TokenToString(node.Kind)))
+			return false
+		}
+		if parent.Kind == ast.KindPropertyDeclaration && parent.AsPropertyDeclaration() != nil && parent.AsPropertyDeclaration().PostfixToken == node {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, scanner.TokenToString(node.Kind)))
+			return false
+		}
+		if parent.Kind == ast.KindMethodDeclaration && parent.AsMethodDeclaration() != nil && parent.AsMethodDeclaration().PostfixToken == node {
+			if node.Kind == ast.KindExclamationToken && parent.Parent.Kind == ast.KindObjectLiteralExpression {
+				// This already gets a grammar error.
+				return false
+			}
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, scanner.TokenToString(node.Kind)))
+			return false
+		}
+		fallthrough
+	case ast.KindConstructor, ast.KindGetAccessor, ast.KindSetAccessor,
+		ast.KindFunctionExpression, ast.KindFunctionDeclaration, ast.KindArrowFunction, ast.KindVariableDeclaration:
+		// Check for type annotations
+		if v.isTypeAnnotation(parent, node) {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.Type_annotations_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+	}
+
+	// Check node-specific constructs
+	switch node.Kind {
+	case ast.KindImportClause:
+		if node.AsImportClause() != nil && node.AsImportClause().IsTypeOnly {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(parent, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "import type"))
+			return false
+		}
+
+	case ast.KindExportDeclaration:
+		if node.AsExportDeclaration() != nil && node.AsExportDeclaration().IsTypeOnly {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "export type"))
+			return false
+		}
+
+	case ast.KindImportSpecifier:
+		if node.AsImportSpecifier() != nil && node.AsImportSpecifier().IsTypeOnly {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "import...type"))
+			return false
+		}
+
+	case ast.KindExportSpecifier:
+		if node.AsExportSpecifier() != nil && node.AsExportSpecifier().IsTypeOnly {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "export...type"))
+			return false
+		}
+
+	case ast.KindImportEqualsDeclaration:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_import_can_only_be_used_in_TypeScript_files))
+		return false
+
+	case ast.KindExportAssignment:
+		if node.AsExportAssignment() != nil && node.AsExportAssignment().IsExportEquals {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_export_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+
+	case ast.KindHeritageClause:
+		if node.AsHeritageClause() != nil && node.AsHeritageClause().Token == ast.KindImplementsKeyword {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_implements_clauses_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+
+	case ast.KindInterfaceDeclaration:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "interface"))
+		return false
+
+	case ast.KindModuleDeclaration:
+		moduleKeyword := "module"
+		if node.AsModuleDeclaration() != nil {
+			switch node.AsModuleDeclaration().Keyword {
+			case ast.KindNamespaceKeyword:
+				moduleKeyword = "namespace"
+			case ast.KindModuleKeyword:
+				moduleKeyword = "module"
+			case ast.KindGlobalKeyword:
+				moduleKeyword = "global"
+			}
+		}
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, moduleKeyword))
+		return false
+
+	case ast.KindTypeAliasDeclaration:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.Type_aliases_can_only_be_used_in_TypeScript_files))
+		return false
+
+	case ast.KindEnumDeclaration:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.X_0_declarations_can_only_be_used_in_TypeScript_files, "enum"))
+		return false
+
+	case ast.KindNonNullExpression:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.Non_null_assertions_can_only_be_used_in_TypeScript_files))
+		return false
+
+	case ast.KindAsExpression:
+		if node.AsAsExpression() != nil {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node.AsAsExpression().Type, diagnostics.Type_assertion_expressions_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+
+	case ast.KindSatisfiesExpression:
+		if node.AsSatisfiesExpression() != nil {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node.AsSatisfiesExpression().Type, diagnostics.Type_satisfaction_expressions_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+
+	case ast.KindConstructor, ast.KindMethodDeclaration, ast.KindFunctionDeclaration:
+		// Check for signature declarations (functions without bodies)
+		if v.isSignatureDeclaration(node) {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(node, diagnostics.Signature_declarations_can_only_be_used_in_TypeScript_files))
+			return false
+		}
+	}
+
+	// Check for type parameters, type arguments, and modifiers
+	v.checkTypeParametersAndModifiers(node)
+
+	// Recursively walk children
+	node.ForEachChild(v.walkNodeForJSDiagnostics)
+
+	return false
+}
+
+// isTypeAnnotation checks if a node is a type annotation in relation to its parent
+func (v *jsDiagnosticsVisitor) isTypeAnnotation(parent *ast.Node, node *ast.Node) bool {
+	switch parent.Kind {
+	case ast.KindFunctionDeclaration:
+		return parent.AsFunctionDeclaration() != nil && parent.AsFunctionDeclaration().Type == node
+	case ast.KindFunctionExpression:
+		return parent.AsFunctionExpression() != nil && parent.AsFunctionExpression().Type == node
+	case ast.KindArrowFunction:
+		return parent.AsArrowFunction() != nil && parent.AsArrowFunction().Type == node
+	case ast.KindMethodDeclaration:
+		return parent.AsMethodDeclaration() != nil && parent.AsMethodDeclaration().Type == node
+	case ast.KindGetAccessor:
+		return parent.AsGetAccessorDeclaration() != nil && parent.AsGetAccessorDeclaration().Type == node
+	case ast.KindSetAccessor:
+		return parent.AsSetAccessorDeclaration() != nil && parent.AsSetAccessorDeclaration().Type == node
+	case ast.KindConstructor:
+		return parent.AsConstructorDeclaration() != nil && parent.AsConstructorDeclaration().Type == node
+	case ast.KindVariableDeclaration:
+		return parent.AsVariableDeclaration() != nil && parent.AsVariableDeclaration().Type == node
+	case ast.KindParameter:
+		return parent.AsParameterDeclaration() != nil && parent.AsParameterDeclaration().Type == node
+	case ast.KindPropertyDeclaration:
+		return parent.AsPropertyDeclaration() != nil && parent.AsPropertyDeclaration().Type == node
+	}
+	return false
+}
+
+// isSignatureDeclaration checks if a node is a signature declaration (function without body)
+func (v *jsDiagnosticsVisitor) isSignatureDeclaration(node *ast.Node) bool {
+	switch node.Kind {
+	case ast.KindFunctionDeclaration:
+		return node.AsFunctionDeclaration() != nil && node.AsFunctionDeclaration().Body == nil
+	case ast.KindMethodDeclaration:
+		return node.AsMethodDeclaration() != nil && node.AsMethodDeclaration().Body == nil
+	case ast.KindConstructor:
+		return node.AsConstructorDeclaration() != nil && node.AsConstructorDeclaration().Body == nil
+	}
+	return false
+}
+
+// checkTypeParametersAndModifiers checks for type parameters, type arguments, and modifiers
+func (v *jsDiagnosticsVisitor) checkTypeParametersAndModifiers(node *ast.Node) {
+	// Bail out early if this node has NodeFlagsReparsed
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return
+	}
+
+	// Check type parameters
+	if typeParams := v.getTypeParameters(node); typeParams != nil {
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNodeList(typeParams, diagnostics.Type_parameter_declarations_can_only_be_used_in_TypeScript_files))
+	}
+
+	// Check type arguments
+	if typeArgs := v.getTypeArguments(node); typeArgs != nil {
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNodeList(typeArgs, diagnostics.Type_arguments_can_only_be_used_in_TypeScript_files))
+	}
+
+	// Check modifiers
+	v.checkModifiers(node)
+}
+
+// getTypeParameters returns the type parameters for a node if it has any non-reparsed ones
+func (v *jsDiagnosticsVisitor) getTypeParameters(node *ast.Node) *ast.NodeList {
+	// Bail out early if this node has NodeFlagsReparsed
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return nil
+	}
+
+	var typeParameters *ast.NodeList
+	switch node.Kind {
+	case ast.KindClassDeclaration:
+		if node.AsClassDeclaration() != nil {
+			typeParameters = node.AsClassDeclaration().TypeParameters
+		}
+	case ast.KindClassExpression:
+		if node.AsClassExpression() != nil {
+			typeParameters = node.AsClassExpression().TypeParameters
+		}
+	case ast.KindMethodDeclaration:
+		if node.AsMethodDeclaration() != nil {
+			typeParameters = node.AsMethodDeclaration().TypeParameters
+		}
+	case ast.KindConstructor:
+		if node.AsConstructorDeclaration() != nil {
+			typeParameters = node.AsConstructorDeclaration().TypeParameters
+		}
+	case ast.KindGetAccessor:
+		if node.AsGetAccessorDeclaration() != nil {
+			typeParameters = node.AsGetAccessorDeclaration().TypeParameters
+		}
+	case ast.KindSetAccessor:
+		if node.AsSetAccessorDeclaration() != nil {
+			typeParameters = node.AsSetAccessorDeclaration().TypeParameters
+		}
+	case ast.KindFunctionExpression:
+		if node.AsFunctionExpression() != nil {
+			typeParameters = node.AsFunctionExpression().TypeParameters
+		}
+	case ast.KindFunctionDeclaration:
+		if node.AsFunctionDeclaration() != nil {
+			typeParameters = node.AsFunctionDeclaration().TypeParameters
+		}
+	case ast.KindArrowFunction:
+		if node.AsArrowFunction() != nil {
+			typeParameters = node.AsArrowFunction().TypeParameters
+		}
+	default:
+		return nil
+	}
+
+	if typeParameters == nil {
+		return nil
+	}
+
+	// Check if all type parameters are reparsed (JSDoc originated)
+	for _, tp := range typeParameters.Nodes {
+		if tp.Flags&ast.NodeFlagsReparsed == 0 {
+			return typeParameters // Found a non-reparsed type parameter, so return the type parameters
+		}
+	}
+
+	return nil // All type parameters are reparsed (JSDoc originated), so this is valid in JS
+}
+
+// hasTypeParameters checks if a node has type parameters
+func (v *jsDiagnosticsVisitor) hasTypeParameters(node *ast.Node) bool {
+	return v.getTypeParameters(node) != nil
+}
+
+// getTypeArguments returns the type arguments for a node if it has any
+func (v *jsDiagnosticsVisitor) getTypeArguments(node *ast.Node) *ast.NodeList {
+	// Bail out early if this node has NodeFlagsReparsed
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return nil
+	}
+
+	var typeArguments *ast.NodeList
+	switch node.Kind {
+	case ast.KindCallExpression:
+		if node.AsCallExpression() != nil {
+			typeArguments = node.AsCallExpression().TypeArguments
+		}
+	case ast.KindNewExpression:
+		if node.AsNewExpression() != nil {
+			typeArguments = node.AsNewExpression().TypeArguments
+		}
+	case ast.KindExpressionWithTypeArguments:
+		if node.AsExpressionWithTypeArguments() != nil {
+			typeArguments = node.AsExpressionWithTypeArguments().TypeArguments
+		}
+	case ast.KindJsxSelfClosingElement:
+		if node.AsJsxSelfClosingElement() != nil {
+			typeArguments = node.AsJsxSelfClosingElement().TypeArguments
+		}
+	case ast.KindJsxOpeningElement:
+		if node.AsJsxOpeningElement() != nil {
+			typeArguments = node.AsJsxOpeningElement().TypeArguments
+		}
+	case ast.KindTaggedTemplateExpression:
+		if node.AsTaggedTemplateExpression() != nil {
+			typeArguments = node.AsTaggedTemplateExpression().TypeArguments
+		}
+	}
+
+	if typeArguments == nil {
+		return nil
+	}
+
+	// Check if all type arguments are reparsed (JSDoc originated)
+	for _, ta := range typeArguments.Nodes {
+		if ta.Flags&ast.NodeFlagsReparsed == 0 {
+			return typeArguments // Found a non-reparsed type argument, so return the type arguments
+		}
+	}
+
+	return nil // All type arguments are reparsed (JSDoc originated), so this is valid in JS
+}
+
+// hasTypeArguments checks if a node has type arguments
+func (v *jsDiagnosticsVisitor) hasTypeArguments(node *ast.Node) bool {
+	// Bail out early if this node has NodeFlagsReparsed
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return false
+	}
+
+	var typeArguments *ast.NodeList
+	switch node.Kind {
+	case ast.KindCallExpression:
+		if node.AsCallExpression() != nil {
+			typeArguments = node.AsCallExpression().TypeArguments
+		}
+	case ast.KindNewExpression:
+		if node.AsNewExpression() != nil {
+			typeArguments = node.AsNewExpression().TypeArguments
+		}
+	case ast.KindExpressionWithTypeArguments:
+		if node.AsExpressionWithTypeArguments() != nil {
+			typeArguments = node.AsExpressionWithTypeArguments().TypeArguments
+		}
+	case ast.KindJsxSelfClosingElement:
+		if node.AsJsxSelfClosingElement() != nil {
+			typeArguments = node.AsJsxSelfClosingElement().TypeArguments
+		}
+	case ast.KindJsxOpeningElement:
+		if node.AsJsxOpeningElement() != nil {
+			typeArguments = node.AsJsxOpeningElement().TypeArguments
+		}
+	case ast.KindTaggedTemplateExpression:
+		if node.AsTaggedTemplateExpression() != nil {
+			typeArguments = node.AsTaggedTemplateExpression().TypeArguments
+		}
+	}
+
+	if typeArguments == nil {
+		return false
+	}
+
+	// Check if all type arguments are reparsed (JSDoc originated)
+	for _, ta := range typeArguments.Nodes {
+		if ta.Flags&ast.NodeFlagsReparsed == 0 {
+			return true // Found a non-reparsed type argument, so this is a TypeScript-only construct
+		}
+	}
+
+	return false // All type arguments are reparsed (JSDoc originated), so this is valid in JS
+}
+
+// checkModifiers checks for TypeScript-only modifiers on various declaration types
+func (v *jsDiagnosticsVisitor) checkModifiers(node *ast.Node) {
+	// Bail out early if this node has NodeFlagsReparsed
+	if node.Flags&ast.NodeFlagsReparsed != 0 {
+		return
+	}
+
+	// Check for TypeScript-only modifiers on various declaration types
+	switch node.Kind {
+	case ast.KindVariableStatement:
+		if node.AsVariableStatement() != nil && node.AsVariableStatement().Modifiers() != nil {
+			v.checkModifierList(node.AsVariableStatement().Modifiers(), true)
+		}
+	case ast.KindPropertyDeclaration:
+		if node.AsPropertyDeclaration() != nil && node.AsPropertyDeclaration().Modifiers() != nil {
+			v.checkPropertyModifiers(node.AsPropertyDeclaration().Modifiers())
+		}
+	case ast.KindParameter:
+		if node.AsParameterDeclaration() != nil && node.AsParameterDeclaration().Modifiers() != nil {
+			v.checkParameterModifiers(node.AsParameterDeclaration().Modifiers())
+		}
+	case ast.KindClassDeclaration:
+		if node.AsClassDeclaration() != nil && node.AsClassDeclaration().Modifiers() != nil {
+			v.checkModifierList(node.AsClassDeclaration().Modifiers(), false)
+		}
+	case ast.KindMethodDeclaration:
+		if node.AsMethodDeclaration() != nil && node.AsMethodDeclaration().Modifiers() != nil {
+			v.checkModifierList(node.AsMethodDeclaration().Modifiers(), false)
+		}
+	case ast.KindFunctionDeclaration:
+		if node.AsFunctionDeclaration() != nil && node.AsFunctionDeclaration().Modifiers() != nil {
+			v.checkModifierList(node.AsFunctionDeclaration().Modifiers(), false)
+		}
+	}
+}
+
+// checkModifierList checks a list of modifiers for TypeScript-only constructs
+func (v *jsDiagnosticsVisitor) checkModifierList(modifiers *ast.ModifierList, isConstValid bool) {
+	if modifiers == nil {
+		return
+	}
+
+	for _, modifier := range modifiers.Nodes {
+		// Bail out early if this modifier has NodeFlagsReparsed
+		if modifier.Flags&ast.NodeFlagsReparsed != 0 {
+			continue
+		}
+		v.checkModifier(modifier, isConstValid)
+	}
+}
+
+// checkPropertyModifiers checks property modifiers for TypeScript-only constructs
+func (v *jsDiagnosticsVisitor) checkPropertyModifiers(modifiers *ast.ModifierList) {
+	if modifiers == nil {
+		return
+	}
+
+	for _, modifier := range modifiers.Nodes {
+		// Bail out early if this modifier has NodeFlagsReparsed
+		if modifier.Flags&ast.NodeFlagsReparsed != 0 {
+			continue
+		}
+		// Property modifiers allow static and accessor, but all other modifiers are invalid
+		switch modifier.Kind {
+		case ast.KindStaticKeyword, ast.KindAccessorKeyword:
+			// These are valid in JavaScript
+			continue
+		default:
+			// All other modifiers are invalid on properties in JavaScript
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(modifier, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, scanner.TokenToString(modifier.Kind)))
+		}
+	}
+}
+
+// checkParameterModifiers checks parameter modifiers for TypeScript-only constructs
+func (v *jsDiagnosticsVisitor) checkParameterModifiers(modifiers *ast.ModifierList) {
+	if modifiers == nil {
+		return
+	}
+
+	for _, modifier := range modifiers.Nodes {
+		// Bail out early if this modifier has NodeFlagsReparsed
+		if modifier.Flags&ast.NodeFlagsReparsed != 0 {
+			continue
+		}
+		// All parameter modifiers are invalid in JavaScript
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(modifier, diagnostics.Parameter_modifiers_can_only_be_used_in_TypeScript_files))
+	}
+}
+
+// checkModifier checks a single modifier for TypeScript-only constructs
+func (v *jsDiagnosticsVisitor) checkModifier(modifier *ast.Node, isConstValid bool) {
+	switch modifier.Kind {
+	case ast.KindConstKeyword:
+		if !isConstValid {
+			v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(modifier, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, "const"))
+		}
+	case ast.KindPublicKeyword, ast.KindPrivateKeyword, ast.KindProtectedKeyword, ast.KindReadonlyKeyword,
+		ast.KindDeclareKeyword, ast.KindAbstractKeyword, ast.KindOverrideKeyword, ast.KindInKeyword, ast.KindOutKeyword:
+		v.diagnostics = append(v.diagnostics, v.createDiagnosticForNode(modifier, diagnostics.The_0_modifier_can_only_be_used_in_TypeScript_files, scanner.TokenToString(modifier.Kind)))
+	case ast.KindStaticKeyword, ast.KindExportKeyword, ast.KindDefaultKeyword, ast.KindAccessorKeyword:
+		// These are valid in JavaScript
+	}
+}
+
+// createDiagnosticForNode creates a diagnostic for a specific node
+func (v *jsDiagnosticsVisitor) createDiagnosticForNode(node *ast.Node, message *diagnostics.Message, args ...any) *ast.Diagnostic {
+	return ast.NewDiagnostic(v.sourceFile, scanner.GetErrorRangeForNode(v.sourceFile, node), message, args...)
+}
+
+// createDiagnosticForNodeList creates a diagnostic for a NodeList
+func (v *jsDiagnosticsVisitor) createDiagnosticForNodeList(nodeList *ast.NodeList, message *diagnostics.Message, args ...any) *ast.Diagnostic {
+	// If the NodeList's location is not set correctly, fall back to using the first node
+	if nodeList.Loc.Pos() == nodeList.Loc.End() && len(nodeList.Nodes) > 0 {
+		// Calculate the range from the first to last node
+		start := nodeList.Nodes[0].Pos()
+		end := nodeList.Nodes[len(nodeList.Nodes)-1].End()
+		return ast.NewDiagnostic(v.sourceFile, core.NewTextRange(start, end), message, args...)
+	}
+	return ast.NewDiagnostic(v.sourceFile, nodeList.Loc, message, args...)
+}
diff --git a/internal/parser/parser.go b/internal/parser/parser.go
index 6cc354802a..ad271ad756 100644
--- a/internal/parser/parser.go
+++ b/internal/parser/parser.go
@@ -381,6 +381,11 @@ func (p *Parser) finishSourceFile(result *ast.SourceFile, isDeclarationFile bool
 	result.SetJSDocCache(p.jsdocCache)
 
 	ast.SetExternalModuleIndicator(result, p.opts.ExternalModuleIndicatorOptions)
+
+	if ast.IsSourceFileJS(result) {
+		// TODO: can these be done while parsing, rather than as a separate pass?
+		result.SetJSSyntacticDiagnostics(getJSSyntacticDiagnosticsForFile(result))
+	}
 }
 
 func (p *Parser) parseToplevelStatement(i int) *ast.Node {
diff --git a/internal/scanner/utilities.go b/internal/scanner/utilities.go
index 06ba7cf666..076523ac9e 100644
--- a/internal/scanner/utilities.go
+++ b/internal/scanner/utilities.go
@@ -65,3 +65,79 @@ func IsIdentifierText(name string, languageVariant core.LanguageVariant) bool {
 func IsIntrinsicJsxName(name string) bool {
 	return len(name) != 0 && (name[0] >= 'a' && name[0] <= 'z' || strings.ContainsRune(name, '-'))
 }
+
+func getErrorRangeForArrowFunction(sourceFile *ast.SourceFile, node *ast.Node) core.TextRange {
+	pos := SkipTrivia(sourceFile.Text(), node.Pos())
+	body := node.AsArrowFunction().Body
+	if body != nil && body.Kind == ast.KindBlock {
+		startLine, _ := GetLineAndCharacterOfPosition(sourceFile, body.Pos())
+		endLine, _ := GetLineAndCharacterOfPosition(sourceFile, body.End())
+		if startLine < endLine {
+			// The arrow function spans multiple lines,
+			// make the error span be the first line, inclusive.
+			return core.NewTextRange(pos, GetEndLinePosition(sourceFile, startLine))
+		}
+	}
+	return core.NewTextRange(pos, node.End())
+}
+
+func GetErrorRangeForNode(sourceFile *ast.SourceFile, node *ast.Node) core.TextRange {
+	errorNode := node
+	switch node.Kind {
+	case ast.KindSourceFile:
+		pos := SkipTrivia(sourceFile.Text(), 0)
+		if pos == len(sourceFile.Text()) {
+			return core.NewTextRange(0, 0)
+		}
+		return GetRangeOfTokenAtPosition(sourceFile, pos)
+	// This list is a work in progress. Add missing node kinds to improve their error spans
+	case ast.KindFunctionDeclaration, ast.KindMethodDeclaration:
+		if node.Flags&ast.NodeFlagsReparsed != 0 {
+			errorNode = node
+			break
+		}
+		fallthrough
+	case ast.KindVariableDeclaration, ast.KindBindingElement, ast.KindClassDeclaration, ast.KindClassExpression, ast.KindInterfaceDeclaration,
+		ast.KindModuleDeclaration, ast.KindEnumDeclaration, ast.KindEnumMember, ast.KindFunctionExpression,
+		ast.KindGetAccessor, ast.KindSetAccessor, ast.KindTypeAliasDeclaration, ast.KindJSTypeAliasDeclaration, ast.KindPropertyDeclaration,
+		ast.KindPropertySignature, ast.KindNamespaceImport:
+		errorNode = ast.GetNameOfDeclaration(node)
+	case ast.KindArrowFunction:
+		return getErrorRangeForArrowFunction(sourceFile, node)
+	case ast.KindCaseClause, ast.KindDefaultClause:
+		start := SkipTrivia(sourceFile.Text(), node.Pos())
+		end := node.End()
+		statements := node.AsCaseOrDefaultClause().Statements.Nodes
+		if len(statements) != 0 {
+			end = statements[0].Pos()
+		}
+		return core.NewTextRange(start, end)
+	case ast.KindReturnStatement, ast.KindYieldExpression:
+		pos := SkipTrivia(sourceFile.Text(), node.Pos())
+		return GetRangeOfTokenAtPosition(sourceFile, pos)
+	case ast.KindSatisfiesExpression:
+		pos := SkipTrivia(sourceFile.Text(), node.AsSatisfiesExpression().Expression.End())
+		return GetRangeOfTokenAtPosition(sourceFile, pos)
+	case ast.KindConstructor:
+		if node.Flags&ast.NodeFlagsReparsed != 0 {
+			errorNode = node
+			break
+		}
+		scanner := GetScannerForSourceFile(sourceFile, node.Pos())
+		start := scanner.TokenStart()
+		for scanner.Token() != ast.KindConstructorKeyword && scanner.Token() != ast.KindStringLiteral && scanner.Token() != ast.KindEndOfFile {
+			scanner.Scan()
+		}
+		return core.NewTextRange(start, scanner.TokenEnd())
+	}
+	if errorNode == nil {
+		// If we don't have a better node, then just set the error on the first token of
+		// construct.
+		return GetRangeOfTokenAtPosition(sourceFile, node.Pos())
+	}
+	pos := errorNode.Pos()
+	if !ast.NodeIsMissing(errorNode) && !ast.IsJsxText(errorNode) {
+		pos = SkipTrivia(sourceFile.Text(), pos)
+	}
+	return core.NewTextRange(pos, errorNode.End())
+}
diff --git a/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.errors.txt b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.errors.txt
new file mode 100644
index 0000000000..0a7a1231e2
--- /dev/null
+++ b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.errors.txt
@@ -0,0 +1,223 @@
+test.js(2,18): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(2,27): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(7,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+test.js(13,6): error TS8008: Type aliases can only be used in TypeScript files.
+test.js(16,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
+test.js(23,8): error TS8006: 'module' declarations can only be used in TypeScript files.
+test.js(28,11): error TS8006: 'namespace' declarations can only be used in TypeScript files.
+test.js(33,13): error TS8013: Non-null assertions can only be used in TypeScript files.
+test.js(36,24): error TS8016: Type assertion expressions can only be used in TypeScript files.
+test.js(39,17): error TS2741: Property 'name' is missing in type '{}' but required in type 'Config'.
+test.js(39,27): error TS8037: Type satisfaction expressions can only be used in TypeScript files.
+test.js(42,1): error TS8006: 'import type' declarations can only be used in TypeScript files.
+test.js(42,31): error TS2307: Cannot find module './other' or its corresponding type declarations.
+test.js(45,1): error TS8006: 'export type' declarations can only be used in TypeScript files.
+test.js(48,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+test.js(48,22): error TS2307: Cannot find module './lib' or its corresponding type declarations.
+test.js(51,1): error TS2309: An export assignment cannot be used in a module with other exported elements.
+test.js(51,1): error TS8003: 'export =' can only be used in TypeScript files.
+test.js(55,5): error TS8009: The 'public' modifier can only be used in TypeScript files.
+test.js(55,18): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(56,5): error TS8009: The 'private' modifier can only be used in TypeScript files.
+test.js(56,18): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(57,5): error TS8009: The 'protected' modifier can only be used in TypeScript files.
+test.js(57,19): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(58,5): error TS8009: The 'readonly' modifier can only be used in TypeScript files.
+test.js(58,21): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(60,17): error TS8012: Parameter modifiers can only be used in TypeScript files.
+test.js(60,27): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(60,35): error TS8012: Parameter modifiers can only be used in TypeScript files.
+test.js(60,46): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(69,25): error TS8009: The '?' modifier can only be used in TypeScript files.
+test.js(69,28): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(74,10): error TS8017: Signature declarations can only be used in TypeScript files.
+test.js(77,18): error TS8004: Type parameter declarations can only be used in TypeScript files.
+test.js(77,24): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(77,28): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(82,19): error TS2693: 'string' only refers to a type, but is being used as a value here.
+test.js(82,27): error TS1109: Expression expected.
+test.js(85,29): error TS8005: 'implements' clauses can only be used in TypeScript files.
+test.js(90,22): error TS8010: Type annotations can only be used in TypeScript files.
+test.js(94,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+
+
+==== test.js (41 errors) ====
+    // Type annotations should be flagged as errors
+    function func(x: number): string {
+                     ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+                              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        return x.toString();
+    }
+    
+    // Interface declarations should be flagged as errors
+    interface Person {
+              ~~~~~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        name: string;
+        age: number;
+    }
+    
+    // Type alias declarations should be flagged as errors
+    type StringOrNumber = string | number;
+         ~~~~~~~~~~~~~~
+!!! error TS8008: Type aliases can only be used in TypeScript files.
+    
+    // Enum declarations should be flagged as errors
+    enum Color {
+         ~~~~~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        Red,
+        Green,
+        Blue
+    }
+    
+    // Module declarations should be flagged as errors
+    module MyModule {
+           ~~~~~~~~
+!!! error TS8006: 'module' declarations can only be used in TypeScript files.
+        export var x = 1;
+    }
+    
+    // Namespace declarations should be flagged as errors
+    namespace MyNamespace {
+              ~~~~~~~~~~~
+!!! error TS8006: 'namespace' declarations can only be used in TypeScript files.
+        export var y = 2;
+    }
+    
+    // Non-null assertions should be flagged as errors
+    let value = getValue()!;
+                ~~~~~~~~~~~
+!!! error TS8013: Non-null assertions can only be used in TypeScript files.
+    
+    // Type assertions should be flagged as errors
+    let result = (value as string).toUpperCase();
+                           ~~~~~~
+!!! error TS8016: Type assertion expressions can only be used in TypeScript files.
+    
+    // Satisfies expressions should be flagged as errors
+    let config = {} satisfies Config;
+                    ~~~~~~~~~
+!!! error TS2741: Property 'name' is missing in type '{}' but required in type 'Config'.
+!!! related TS2728 test.js:95:5: 'name' is declared here.
+                              ~~~~~~
+!!! error TS8037: Type satisfaction expressions can only be used in TypeScript files.
+    
+    // Import type should be flagged as errors
+    import type { SomeType } from './other';
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8006: 'import type' declarations can only be used in TypeScript files.
+                                  ~~~~~~~~~
+!!! error TS2307: Cannot find module './other' or its corresponding type declarations.
+    
+    // Export type should be flagged as errors
+    export type { SomeType };
+    ~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8006: 'export type' declarations can only be used in TypeScript files.
+    
+    // Import equals should be flagged as errors
+    import lib = require('./lib');
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+                         ~~~~~~~
+!!! error TS2307: Cannot find module './lib' or its corresponding type declarations.
+    
+    // Export equals should be flagged as errors
+    export = MyModule;
+    ~~~~~~~~~~~~~~~~~~
+!!! error TS2309: An export assignment cannot be used in a module with other exported elements.
+    ~~~~~~~~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
+    
+    // TypeScript modifiers should be flagged as errors
+    class MyClass {
+        public name: string;
+        ~~~~~~
+!!! error TS8009: The 'public' modifier can only be used in TypeScript files.
+                     ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        private age: number;
+        ~~~~~~~
+!!! error TS8009: The 'private' modifier can only be used in TypeScript files.
+                     ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        protected id: number;
+        ~~~~~~~~~
+!!! error TS8009: The 'protected' modifier can only be used in TypeScript files.
+                      ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        readonly value: number;
+        ~~~~~~~~
+!!! error TS8009: The 'readonly' modifier can only be used in TypeScript files.
+                        ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        
+        constructor(public x: number, private y: number) {
+                    ~~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
+                              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+                                      ~~~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
+                                                 ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+            this.name = '';
+            this.age = 0;
+            this.id = 0;
+            this.value = 0;
+        }
+    }
+    
+    // Optional parameters should be flagged as errors
+    function optionalParam(x?: number) {
+                            ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
+                               ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        return x || 0;
+    }
+    
+    // Signature declarations should be flagged as errors
+    function signatureOnly(x: number): string;
+             ~~~~~~~~~~~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    
+    // Type parameters should be flagged as errors
+    function generic<T>(x: T): T {
+                     ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
+                           ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+                               ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        return x;
+    }
+    
+    // Type arguments should be flagged as errors
+    let array = Array<string>();
+                      ~~~~~~
+!!! error TS2693: 'string' only refers to a type, but is being used as a value here.
+                              ~
+!!! error TS1109: Expression expected.
+    
+    // Implements clause should be flagged as errors
+    class MyClassWithImplements implements Person {
+                                ~~~~~~~~~~~~~~~~~
+!!! error TS8005: 'implements' clauses can only be used in TypeScript files.
+        name = '';
+        age = 0;
+    }
+    
+    function getValue(): any {
+                         ~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        return null;
+    }
+    
+    interface Config {
+              ~~~~~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        name: string;
+    }
\ No newline at end of file
diff --git a/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.symbols b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.symbols
new file mode 100644
index 0000000000..a6b8708dea
--- /dev/null
+++ b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.symbols
@@ -0,0 +1,189 @@
+//// [tests/cases/compiler/jsSyntacticDiagnostics.ts] ////
+
+=== test.js ===
+// Type annotations should be flagged as errors
+function func(x: number): string {
+>func : Symbol(func, Decl(test.js, 0, 0))
+>x : Symbol(x, Decl(test.js, 1, 14))
+
+    return x.toString();
+>x.toString : Symbol(toString, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(test.js, 1, 14))
+>toString : Symbol(toString, Decl(lib.es5.d.ts, --, --))
+}
+
+// Interface declarations should be flagged as errors
+interface Person {
+>Person : Symbol(Person, Decl(test.js, 3, 1))
+
+    name: string;
+>name : Symbol(name, Decl(test.js, 6, 18))
+
+    age: number;
+>age : Symbol(age, Decl(test.js, 7, 17))
+}
+
+// Type alias declarations should be flagged as errors
+type StringOrNumber = string | number;
+>StringOrNumber : Symbol(StringOrNumber, Decl(test.js, 9, 1))
+
+// Enum declarations should be flagged as errors
+enum Color {
+>Color : Symbol(Color, Decl(test.js, 12, 38))
+
+    Red,
+>Red : Symbol(Red, Decl(test.js, 15, 12))
+
+    Green,
+>Green : Symbol(Green, Decl(test.js, 16, 8))
+
+    Blue
+>Blue : Symbol(Blue, Decl(test.js, 17, 10))
+}
+
+// Module declarations should be flagged as errors
+module MyModule {
+>MyModule : Symbol(MyModule, Decl(test.js, 19, 1))
+
+    export var x = 1;
+>x : Symbol(x, Decl(test.js, 23, 14))
+}
+
+// Namespace declarations should be flagged as errors
+namespace MyNamespace {
+>MyNamespace : Symbol(MyNamespace, Decl(test.js, 24, 1))
+
+    export var y = 2;
+>y : Symbol(y, Decl(test.js, 28, 14))
+}
+
+// Non-null assertions should be flagged as errors
+let value = getValue()!;
+>value : Symbol(value, Decl(test.js, 32, 3))
+>getValue : Symbol(getValue, Decl(test.js, 87, 1))
+
+// Type assertions should be flagged as errors
+let result = (value as string).toUpperCase();
+>result : Symbol(result, Decl(test.js, 35, 3))
+>(value as string).toUpperCase : Symbol(toUpperCase, Decl(lib.es5.d.ts, --, --))
+>value : Symbol(value, Decl(test.js, 32, 3))
+>toUpperCase : Symbol(toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+// Satisfies expressions should be flagged as errors
+let config = {} satisfies Config;
+>config : Symbol(config, Decl(test.js, 38, 3))
+>Config : Symbol(Config, Decl(test.js, 91, 1))
+
+// Import type should be flagged as errors
+import type { SomeType } from './other';
+>SomeType : Symbol(SomeType, Decl(test.js, 41, 13))
+
+// Export type should be flagged as errors
+export type { SomeType };
+>SomeType : Symbol(SomeType, Decl(test.js, 44, 13))
+
+// Import equals should be flagged as errors
+import lib = require('./lib');
+>lib : Symbol(lib, Decl(test.js, 44, 25))
+
+// Export equals should be flagged as errors
+export = MyModule;
+>MyModule : Symbol(MyModule, Decl(test.js, 19, 1))
+
+// TypeScript modifiers should be flagged as errors
+class MyClass {
+>MyClass : Symbol(MyClass, Decl(test.js, 50, 18))
+
+    public name: string;
+>name : Symbol(name, Decl(test.js, 53, 15))
+
+    private age: number;
+>age : Symbol(age, Decl(test.js, 54, 24))
+
+    protected id: number;
+>id : Symbol(id, Decl(test.js, 55, 24))
+
+    readonly value: number;
+>value : Symbol(value, Decl(test.js, 56, 25))
+    
+    constructor(public x: number, private y: number) {
+>x : Symbol(x, Decl(test.js, 59, 16))
+>y : Symbol(y, Decl(test.js, 59, 33))
+
+        this.name = '';
+>this.name : Symbol(name, Decl(test.js, 53, 15))
+>this : Symbol(MyClass, Decl(test.js, 50, 18))
+>name : Symbol(name, Decl(test.js, 53, 15))
+
+        this.age = 0;
+>this.age : Symbol(age, Decl(test.js, 54, 24))
+>this : Symbol(MyClass, Decl(test.js, 50, 18))
+>age : Symbol(age, Decl(test.js, 54, 24))
+
+        this.id = 0;
+>this.id : Symbol(id, Decl(test.js, 55, 24))
+>this : Symbol(MyClass, Decl(test.js, 50, 18))
+>id : Symbol(id, Decl(test.js, 55, 24))
+
+        this.value = 0;
+>this.value : Symbol(value, Decl(test.js, 56, 25))
+>this : Symbol(MyClass, Decl(test.js, 50, 18))
+>value : Symbol(value, Decl(test.js, 56, 25))
+    }
+}
+
+// Optional parameters should be flagged as errors
+function optionalParam(x?: number) {
+>optionalParam : Symbol(optionalParam, Decl(test.js, 65, 1))
+>x : Symbol(x, Decl(test.js, 68, 23))
+
+    return x || 0;
+>x : Symbol(x, Decl(test.js, 68, 23))
+}
+
+// Signature declarations should be flagged as errors
+function signatureOnly(x: number): string;
+>signatureOnly : Symbol(signatureOnly, Decl(test.js, 70, 1))
+>x : Symbol(x, Decl(test.js, 73, 23))
+
+// Type parameters should be flagged as errors
+function generic<T>(x: T): T {
+>generic : Symbol(generic, Decl(test.js, 73, 42))
+>T : Symbol(T, Decl(test.js, 76, 17))
+>x : Symbol(x, Decl(test.js, 76, 20))
+>T : Symbol(T, Decl(test.js, 76, 17))
+>T : Symbol(T, Decl(test.js, 76, 17))
+
+    return x;
+>x : Symbol(x, Decl(test.js, 76, 20))
+}
+
+// Type arguments should be flagged as errors
+let array = Array<string>();
+>array : Symbol(array, Decl(test.js, 81, 3))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+// Implements clause should be flagged as errors
+class MyClassWithImplements implements Person {
+>MyClassWithImplements : Symbol(MyClassWithImplements, Decl(test.js, 81, 28))
+>Person : Symbol(Person, Decl(test.js, 3, 1))
+
+    name = '';
+>name : Symbol(name, Decl(test.js, 84, 47))
+
+    age = 0;
+>age : Symbol(age, Decl(test.js, 85, 14))
+}
+
+function getValue(): any {
+>getValue : Symbol(getValue, Decl(test.js, 87, 1))
+
+    return null;
+}
+
+interface Config {
+>Config : Symbol(Config, Decl(test.js, 91, 1))
+
+    name: string;
+>name : Symbol(name, Decl(test.js, 93, 18))
+}
diff --git a/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.types b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.types
new file mode 100644
index 0000000000..48707ff263
--- /dev/null
+++ b/testdata/baselines/reference/compiler/jsSyntacticDiagnostics.types
@@ -0,0 +1,207 @@
+//// [tests/cases/compiler/jsSyntacticDiagnostics.ts] ////
+
+=== test.js ===
+// Type annotations should be flagged as errors
+function func(x: number): string {
+>func : (x: number) => string
+>x : number
+
+    return x.toString();
+>x.toString() : string
+>x.toString : (radix?: number) => string
+>x : number
+>toString : (radix?: number) => string
+}
+
+// Interface declarations should be flagged as errors
+interface Person {
+    name: string;
+>name : string
+
+    age: number;
+>age : number
+}
+
+// Type alias declarations should be flagged as errors
+type StringOrNumber = string | number;
+>StringOrNumber : StringOrNumber
+
+// Enum declarations should be flagged as errors
+enum Color {
+>Color : Color
+
+    Red,
+>Red : Color.Red
+
+    Green,
+>Green : Color.Green
+
+    Blue
+>Blue : Color.Blue
+}
+
+// Module declarations should be flagged as errors
+module MyModule {
+>MyModule : typeof MyModule
+
+    export var x = 1;
+>x : number
+>1 : 1
+}
+
+// Namespace declarations should be flagged as errors
+namespace MyNamespace {
+>MyNamespace : typeof MyNamespace
+
+    export var y = 2;
+>y : number
+>2 : 2
+}
+
+// Non-null assertions should be flagged as errors
+let value = getValue()!;
+>value : any
+>getValue()! : any
+>getValue() : any
+>getValue : () => any
+
+// Type assertions should be flagged as errors
+let result = (value as string).toUpperCase();
+>result : string
+>(value as string).toUpperCase() : string
+>(value as string).toUpperCase : () => string
+>(value as string) : string
+>value as string : string
+>value : any
+>toUpperCase : () => string
+
+// Satisfies expressions should be flagged as errors
+let config = {} satisfies Config;
+>config : {}
+>{} satisfies Config : {}
+>{} : {}
+
+// Import type should be flagged as errors
+import type { SomeType } from './other';
+>SomeType : any
+
+// Export type should be flagged as errors
+export type { SomeType };
+>SomeType : any
+
+// Import equals should be flagged as errors
+import lib = require('./lib');
+>lib : any
+
+// Export equals should be flagged as errors
+export = MyModule;
+>MyModule : typeof MyModule
+
+// TypeScript modifiers should be flagged as errors
+class MyClass {
+>MyClass : MyClass
+
+    public name: string;
+>name : string
+
+    private age: number;
+>age : number
+
+    protected id: number;
+>id : number
+
+    readonly value: number;
+>value : number
+    
+    constructor(public x: number, private y: number) {
+>x : number
+>y : number
+
+        this.name = '';
+>this.name = '' : ""
+>this.name : string
+>this : this
+>name : string
+>'' : ""
+
+        this.age = 0;
+>this.age = 0 : 0
+>this.age : number
+>this : this
+>age : number
+>0 : 0
+
+        this.id = 0;
+>this.id = 0 : 0
+>this.id : number
+>this : this
+>id : number
+>0 : 0
+
+        this.value = 0;
+>this.value = 0 : 0
+>this.value : number
+>this : this
+>value : number
+>0 : 0
+    }
+}
+
+// Optional parameters should be flagged as errors
+function optionalParam(x?: number) {
+>optionalParam : (x?: number) => number
+>x : number
+
+    return x || 0;
+>x || 0 : number
+>x : number
+>0 : 0
+}
+
+// Signature declarations should be flagged as errors
+function signatureOnly(x: number): string;
+>signatureOnly : (x: number) => string
+>x : number
+
+// Type parameters should be flagged as errors
+function generic<T>(x: T): T {
+>generic : <T>(x: T) => T
+>x : T
+
+    return x;
+>x : T
+}
+
+// Type arguments should be flagged as errors
+let array = Array<string>();
+>array : boolean
+>Array<string>() : boolean
+>Array<string : boolean
+>Array : ArrayConstructor
+>string : any
+>() : any
+> : any
+
+// Implements clause should be flagged as errors
+class MyClassWithImplements implements Person {
+>MyClassWithImplements : MyClassWithImplements
+
+    name = '';
+>name : string
+>'' : ""
+
+    age = 0;
+>age : number
+>0 : 0
+}
+
+function getValue(): any {
+>getValue : () => any
+
+    return null;
+}
+
+interface Config {
+    name: string;
+>name : string
+}
diff --git a/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=false).errors.txt b/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=false).errors.txt
index a799d98368..7e0c1775a3 100644
--- a/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=false).errors.txt
+++ b/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=false).errors.txt
@@ -1,5 +1,7 @@
 error TS5055: Cannot write file 'b.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+b.js(9,27): error TS8011: Type arguments can only be used in TypeScript files.
+b.js(15,27): error TS8011: Type arguments can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'b.js' because it would overwrite input file.
@@ -7,7 +9,7 @@ error TS5055: Cannot write file 'b.js' because it would overwrite input file.
 ==== a.ts (0 errors) ====
     export class A<T> {}
     
-==== b.js (0 errors) ====
+==== b.js (2 errors) ====
     import { A } from './a.js';
     
     export class B1 extends A {
@@ -17,12 +19,16 @@ error TS5055: Cannot write file 'b.js' because it would overwrite input file.
     }
     
     export class B2 extends A<string> {
+                              ~~~~~~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
         constructor() {
             super();
         }
     }
     
     export class B3 extends A<string, string> {
+                              ~~~~~~~~~~~~~~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
         constructor() {
             super();
         }
diff --git a/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=true).errors.txt b/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=true).errors.txt
index 1cc1d93aa0..3d32450ed8 100644
--- a/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=true).errors.txt
+++ b/testdata/baselines/reference/compiler/superCallInJSWithWrongBaseTypeArgumentCount1(strict=true).errors.txt
@@ -1,7 +1,9 @@
 error TS5055: Cannot write file 'b.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 b.js(3,25): error TS8026: Expected A<T> type arguments; provide these with an '@extends' tag.
+b.js(9,27): error TS8011: Type arguments can only be used in TypeScript files.
 b.js(15,25): error TS8026: Expected A<T> type arguments; provide these with an '@extends' tag.
+b.js(15,27): error TS8011: Type arguments can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'b.js' because it would overwrite input file.
@@ -9,7 +11,7 @@ b.js(15,25): error TS8026: Expected A<T> type arguments; provide these with an '
 ==== a.ts (0 errors) ====
     export class A<T> {}
     
-==== b.js (2 errors) ====
+==== b.js (4 errors) ====
     import { A } from './a.js';
     
     export class B1 extends A {
@@ -21,6 +23,8 @@ b.js(15,25): error TS8026: Expected A<T> type arguments; provide these with an '
     }
     
     export class B2 extends A<string> {
+                              ~~~~~~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
         constructor() {
             super();
         }
@@ -29,6 +33,8 @@ b.js(15,25): error TS8026: Expected A<T> type arguments; provide these with an '
     export class B3 extends A<string, string> {
                             ~~~~~~~~~~~~~~~~~
 !!! error TS8026: Expected A<T> type arguments; provide these with an '@extends' tag.
+                              ~~~~~~~~~~~~~~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
         constructor() {
             super();
         }
diff --git a/testdata/baselines/reference/submodule/compiler/ambientPropertyDeclarationInJs.errors.txt b/testdata/baselines/reference/submodule/compiler/ambientPropertyDeclarationInJs.errors.txt
index 1ce833f6c1..c23b932b5f 100644
--- a/testdata/baselines/reference/submodule/compiler/ambientPropertyDeclarationInJs.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/ambientPropertyDeclarationInJs.errors.txt
@@ -1,8 +1,10 @@
 /test.js(3,9): error TS2322: Type '{}' is not assignable to type 'string'.
+/test.js(6,5): error TS8009: The 'declare' modifier can only be used in TypeScript files.
+/test.js(6,19): error TS8010: Type annotations can only be used in TypeScript files.
 /test.js(9,19): error TS2339: Property 'foo' does not exist on type 'string'.
 
 
-==== /test.js (2 errors) ====
+==== /test.js (4 errors) ====
     class Foo {
         constructor() {
             this.prop = {};
@@ -11,6 +13,10 @@
         }
     
         declare prop: string;
+        ~~~~~~~
+!!! error TS8009: The 'declare' modifier can only be used in TypeScript files.
+                      ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
     
         method() {
             this.prop.foo
diff --git a/testdata/baselines/reference/submodule/compiler/decoratorInJsFile.errors.txt b/testdata/baselines/reference/submodule/compiler/decoratorInJsFile.errors.txt
new file mode 100644
index 0000000000..520dc4d9d0
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/decoratorInJsFile.errors.txt
@@ -0,0 +1,12 @@
+a.js(3,12): error TS8010: Type annotations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    @SomeDecorator
+    class SomeClass {
+        foo(x: number) {
+               ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    
+        }
+    }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/decoratorInJsFile1.errors.txt b/testdata/baselines/reference/submodule/compiler/decoratorInJsFile1.errors.txt
new file mode 100644
index 0000000000..520dc4d9d0
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/decoratorInJsFile1.errors.txt
@@ -0,0 +1,12 @@
+a.js(3,12): error TS8010: Type annotations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    @SomeDecorator
+    class SomeClass {
+        foo(x: number) {
+               ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    
+        }
+    }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt b/testdata/baselines/reference/submodule/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt
index a044985514..a4e9026a3a 100644
--- a/testdata/baselines/reference/submodule/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt
@@ -1,6 +1,10 @@
+BaseB.js(2,24): error TS8004: Type parameter declarations can only be used in TypeScript files.
 BaseB.js(2,25): error TS1005: ',' expected.
 BaseB.js(3,14): error TS2304: Cannot find name 'Class'.
+BaseB.js(3,14): error TS8010: Type annotations can only be used in TypeScript files.
 BaseB.js(4,25): error TS2304: Cannot find name 'Class'.
+BaseB.js(4,25): error TS8010: Type annotations can only be used in TypeScript files.
+SubB.js(3,41): error TS8011: Type arguments can only be used in TypeScript files.
 
 
 ==== BaseA.js (0 errors) ====
@@ -10,24 +14,32 @@ BaseB.js(4,25): error TS2304: Cannot find name 'Class'.
     import BaseA from './BaseA';
     export default class SubA extends BaseA {
     }
-==== BaseB.js (3 errors) ====
+==== BaseB.js (6 errors) ====
     import BaseA from './BaseA';
     export default class B<T: BaseA> {
+                           ~~~~~~~~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
                             ~
 !!! error TS1005: ',' expected.
         _AClass: Class<T>;
                  ~~~~~
 !!! error TS2304: Cannot find name 'Class'.
+                 ~~~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
         constructor(AClass: Class<T>) {
                             ~~~~~
 !!! error TS2304: Cannot find name 'Class'.
+                            ~~~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
             this._AClass = AClass;
         }
     }
-==== SubB.js (0 errors) ====
+==== SubB.js (1 errors) ====
     import SubA from './SubA';
     import BaseB from './BaseB';
     export default class SubB extends BaseB<SubA> {
+                                            ~~~~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
         constructor() {
             super(SubA);
         }
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationAbstractModifier.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationAbstractModifier.errors.txt
index dd02778d17..fecf44cbf1 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationAbstractModifier.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationAbstractModifier.errors.txt
@@ -1,10 +1,16 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,1): error TS8009: The 'abstract' modifier can only be used in TypeScript files.
+a.js(2,5): error TS8009: The 'abstract' modifier can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
+==== a.js (2 errors) ====
     abstract class c {
+    ~~~~~~~~
+!!! error TS8009: The 'abstract' modifier can only be used in TypeScript files.
         abstract x;
+        ~~~~~~~~
+!!! error TS8009: The 'abstract' modifier can only be used in TypeScript files.
     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt
index 37eb955360..8861140309 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,1): error TS8009: The 'declare' modifier can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    declare var v;
\ No newline at end of file
+==== a.js (1 errors) ====
+    declare var v;
+    ~~~~~~~
+!!! error TS8009: The 'declare' modifier can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt
new file mode 100644
index 0000000000..c2eefe3d28
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt
@@ -0,0 +1,10 @@
+a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    class A {
+      constructor();
+      ~~~~~~~~~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationEnumSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationEnumSyntax.errors.txt
index c5ff5ff9ac..bf1bafd05c 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationEnumSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationEnumSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    enum E { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    enum E { }
+         ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt
index f141ba456e..8c14639397 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,1): error TS8003: 'export =' can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    export = b;
\ No newline at end of file
+==== a.js (1 errors) ====
+    export = b;
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt
new file mode 100644
index 0000000000..1c10528f03
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt
@@ -0,0 +1,8 @@
+a.js(1,10): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    function foo();
+             ~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt
index 553b43effa..842119639a 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,9): error TS8005: 'implements' clauses can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    class C implements D { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    class C implements D { }
+            ~~~~~~~~~~~~
+!!! error TS8005: 'implements' clauses can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationImportEqualsSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationImportEqualsSyntax.errors.txt
index b172ac39e3..062ec765e5 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationImportEqualsSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationImportEqualsSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    import a = b;
\ No newline at end of file
+==== a.js (1 errors) ====
+    import a = b;
+    ~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationInterfaceSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationInterfaceSyntax.errors.txt
index e2fb064081..e4d6397f82 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationInterfaceSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationInterfaceSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    interface I { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    interface I { }
+              ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt
new file mode 100644
index 0000000000..470da0781c
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt
@@ -0,0 +1,10 @@
+a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    class A {
+      foo();
+      ~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationModuleSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationModuleSyntax.errors.txt
index 06a0de832e..efda02b1ad 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationModuleSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationModuleSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,8): error TS8006: 'module' declarations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    module M { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    module M { }
+           ~
+!!! error TS8006: 'module' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationNonNullAssertion.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationNonNullAssertion.errors.txt
index ac3f77f625..32c9cb870e 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationNonNullAssertion.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationNonNullAssertion.errors.txt
@@ -1,11 +1,14 @@
 error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
+/src/a.js(1,1): error TS8013: Non-null assertions can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 !!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-==== /src/a.js (0 errors) ====
+==== /src/a.js (1 errors) ====
     0!
+    ~~
+!!! error TS8013: Non-null assertions can only be used in TypeScript files.
     
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt
index 667303c917..c9114536f2 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt
@@ -1,12 +1,18 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(2,8): error TS8009: The '?' modifier can only be used in TypeScript files.
+a.js(4,8): error TS8009: The '?' modifier can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
+==== a.js (2 errors) ====
     class C {
         foo?() {
+           ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
         }
         bar? = 1; 
+           ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalParameter.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalParameter.errors.txt
index 4bfa438887..120e92667f 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalParameter.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationOptionalParameter.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,13): error TS8009: The '?' modifier can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    function F(p?) { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    function F(p?) { }
+                ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt
index 63a92e4e09..c14f1e86e9 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt
@@ -1,11 +1,14 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(2,5): error TS8009: The 'public' modifier can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
+==== a.js (1 errors) ====
     class C {
         public foo() {
+        ~~~~~~
+!!! error TS8009: The 'public' modifier can only be used in TypeScript files.
         }
     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicParameterModifier.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicParameterModifier.errors.txt
index c1570e779e..f08d7593a2 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicParameterModifier.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationPublicParameterModifier.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,23): error TS8012: Parameter modifiers can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    class C { constructor(public x) { }}
\ No newline at end of file
+==== a.js (1 errors) ====
+    class C { constructor(public x) { }}
+                          ~~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt
index a3f6c03f55..d9b9da98fb 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    function F(): number { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    function F(): number { }
+                  ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAliasSyntax.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAliasSyntax.errors.txt
index d2178618fc..4eb4eea95e 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAliasSyntax.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAliasSyntax.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,6): error TS8008: Type aliases can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    type a = b;
\ No newline at end of file
+==== a.js (1 errors) ====
+    type a = b;
+         ~
+!!! error TS8008: Type aliases can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAssertions.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAssertions.errors.txt
index e176d8159b..852f133911 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAssertions.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeAssertions.errors.txt
@@ -1,6 +1,7 @@
 error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
+/src/a.js(1,6): error TS8016: Type assertion expressions can only be used in TypeScript files.
 /src/a.js(2,10): error TS17008: JSX element 'string' has no corresponding closing tag.
 /src/a.js(3,1): error TS1005: '</' expected.
 
@@ -8,8 +9,10 @@ error TS5102: Option 'outFile' has been removed. Please remove it from your conf
 !!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 !!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-==== /src/a.js (2 errors) ====
+==== /src/a.js (3 errors) ====
     0 as number;
+         ~~~~~~
+!!! error TS8016: Type assertion expressions can only be used in TypeScript files.
     var v = <string>undefined;
              ~~~~~~
 !!! error TS17008: JSX element 'string' has no corresponding closing tag.
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeOfParameter.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeOfParameter.errors.txt
index 555cd30eaa..15ff6e7d06 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeOfParameter.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeOfParameter.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    function F(a: number) { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    function F(a: number) { }
+                  ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt
index 4711eb262c..31366a04b9 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,9): error TS8004: Type parameter declarations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    class C<T> { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    class C<T> { }
+            ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt
new file mode 100644
index 0000000000..9adc8c87bb
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt
@@ -0,0 +1,8 @@
+a.js(1,19): error TS8004: Type parameter declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    const Bar = class<T> {};
+                      ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt
index 8c0597d88c..831e7c8003 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,12): error TS8004: Type parameter declarations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    function F<T>() { }
\ No newline at end of file
+==== a.js (1 errors) ====
+    function F<T>() { }
+               ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt
index 2a6c537beb..80f421c50d 100644
--- a/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt
@@ -1,8 +1,11 @@
 error TS5055: Cannot write file 'a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
+a.js(1,8): error TS8010: Type annotations can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
-==== a.js (0 errors) ====
-    var v: () => number;
\ No newline at end of file
+==== a.js (1 errors) ====
+    var v: () => number;
+           ~~~~~~~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/jsdocTypedefNoCrash2.errors.txt b/testdata/baselines/reference/submodule/compiler/jsdocTypedefNoCrash2.errors.txt
new file mode 100644
index 0000000000..6239c728e6
--- /dev/null
+++ b/testdata/baselines/reference/submodule/compiler/jsdocTypedefNoCrash2.errors.txt
@@ -0,0 +1,12 @@
+export.js(1,13): error TS8008: Type aliases can only be used in TypeScript files.
+
+
+==== export.js (1 errors) ====
+    export type foo = 5;
+                ~~~
+!!! error TS8008: Type aliases can only be used in TypeScript files.
+    /**
+     * @typedef {{
+     * }}
+     */
+    export const foo = 5;
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/compiler/modulePreserve4.errors.txt b/testdata/baselines/reference/submodule/compiler/modulePreserve4.errors.txt
index a0ef9a937d..993845bad6 100644
--- a/testdata/baselines/reference/submodule/compiler/modulePreserve4.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/modulePreserve4.errors.txt
@@ -8,6 +8,7 @@
 /main2.mts(14,8): error TS1192: Module '"/e"' has no default export.
 /main3.cjs(1,10): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
 /main3.cjs(1,13): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
+/main3.cjs(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 /main3.cjs(5,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
 /main3.cjs(8,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
 /main3.cjs(10,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
@@ -112,13 +113,15 @@
     import g1 from "./g"; // { default: 0 }
     import g2 = require("./g"); // { default: 0 }
     
-==== /main3.cjs (8 errors) ====
+==== /main3.cjs (9 errors) ====
     import { x, y } from "./a"; // No y
              ~
 !!! error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
                 ~
 !!! error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
     import a1 = require("./a"); // Error in JS
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     const a2 = require("./a"); // { x: 0 }
     
     import b1 from "./b"; // 0
diff --git a/testdata/baselines/reference/submodule/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt b/testdata/baselines/reference/submodule/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt
index 914c08744a..3824bc8325 100644
--- a/testdata/baselines/reference/submodule/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt
+++ b/testdata/baselines/reference/submodule/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt
@@ -1,16 +1,22 @@
+a.js(1,8): error TS8006: 'module' declarations can only be used in TypeScript files.
 a.js(2,5): error TS2331: 'this' cannot be referenced in a module or namespace body.
+b.js(1,11): error TS8006: 'namespace' declarations can only be used in TypeScript files.
 b.js(2,5): error TS2331: 'this' cannot be referenced in a module or namespace body.
 
 
-==== a.js (1 errors) ====
+==== a.js (2 errors) ====
     module foo {
+           ~~~
+!!! error TS8006: 'module' declarations can only be used in TypeScript files.
         this.bar = 4;
         ~~~~
 !!! error TS2331: 'this' cannot be referenced in a module or namespace body.
     }
     
-==== b.js (1 errors) ====
+==== b.js (2 errors) ====
     namespace blah {
+              ~~~~
+!!! error TS8006: 'namespace' declarations can only be used in TypeScript files.
         this.prop = 42;
         ~~~~
 !!! error TS2331: 'this' cannot be referenced in a module or namespace body.
diff --git a/testdata/baselines/reference/submodule/conformance/exportNamespace_js.errors.txt b/testdata/baselines/reference/submodule/conformance/exportNamespace_js.errors.txt
index bea8c5ca84..245e895c73 100644
--- a/testdata/baselines/reference/submodule/conformance/exportNamespace_js.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/exportNamespace_js.errors.txt
@@ -1,11 +1,14 @@
+b.js(1,1): error TS8006: 'export type' declarations can only be used in TypeScript files.
 c.js(2,1): error TS1362: 'A' cannot be used as a value because it was exported using 'export type'.
 
 
 ==== a.js (0 errors) ====
     export class A {}
     
-==== b.js (0 errors) ====
+==== b.js (1 errors) ====
     export type * from './a';
+    ~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8006: 'export type' declarations can only be used in TypeScript files.
     
 ==== c.js (1 errors) ====
     import { A } from './b';
diff --git a/testdata/baselines/reference/submodule/conformance/exportSpecifiers_js.errors.txt b/testdata/baselines/reference/submodule/conformance/exportSpecifiers_js.errors.txt
new file mode 100644
index 0000000000..cb436125a0
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/exportSpecifiers_js.errors.txt
@@ -0,0 +1,9 @@
+a.js(2,10): error TS8006: 'export...type' declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    const foo = 0;
+    export { type foo };
+             ~~~~~~~~
+!!! error TS8006: 'export...type' declarations can only be used in TypeScript files.
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/grammarErrors.errors.txt b/testdata/baselines/reference/submodule/conformance/grammarErrors.errors.txt
index 599518b3b4..bf1009be1c 100644
--- a/testdata/baselines/reference/submodule/conformance/grammarErrors.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/grammarErrors.errors.txt
@@ -1,6 +1,8 @@
 error TS5055: Cannot write file '/a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 error TS5056: Cannot write file '/a.js' because it would be overwritten by multiple input files.
+/a.js(1,1): error TS8006: 'import type' declarations can only be used in TypeScript files.
+/a.js(2,1): error TS8006: 'export type' declarations can only be used in TypeScript files.
 /b.ts(1,8): error TS1363: A type-only import can specify a default import or named bindings, but not both.
 /c.ts(4,1): error TS1392: An import alias cannot use 'import type'
 
@@ -18,9 +20,13 @@ error TS5056: Cannot write file '/a.js' because it would be overwritten by multi
            ~~~~~~~~~~~~~~~~
 !!! error TS1363: A type-only import can specify a default import or named bindings, but not both.
     
-==== /a.js (0 errors) ====
+==== /a.js (2 errors) ====
     import type A from './a';
+    ~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8006: 'import type' declarations can only be used in TypeScript files.
     export type { A };
+    ~~~~~~~~~~~~~~~~~~
+!!! error TS8006: 'export type' declarations can only be used in TypeScript files.
     
 ==== /c.ts (1 errors) ====
     namespace ns {
diff --git a/testdata/baselines/reference/submodule/conformance/importSpecifiers_js.errors.txt b/testdata/baselines/reference/submodule/conformance/importSpecifiers_js.errors.txt
new file mode 100644
index 0000000000..c934c298b2
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/importSpecifiers_js.errors.txt
@@ -0,0 +1,11 @@
+a.js(1,10): error TS8006: 'import...type' declarations can only be used in TypeScript files.
+
+
+==== a.ts (0 errors) ====
+    export interface A {}
+    
+==== a.js (1 errors) ====
+    import { type A } from "./a";
+             ~~~~~~
+!!! error TS8006: 'import...type' declarations can only be used in TypeScript files.
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/jsDeclarationsClassesErr.errors.txt b/testdata/baselines/reference/submodule/conformance/jsDeclarationsClassesErr.errors.txt
new file mode 100644
index 0000000000..548135e903
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/jsDeclarationsClassesErr.errors.txt
@@ -0,0 +1,136 @@
+index.js(4,16): error TS8004: Type parameter declarations can only be used in TypeScript files.
+index.js(5,12): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(8,16): error TS8004: Type parameter declarations can only be used in TypeScript files.
+index.js(8,29): error TS8011: Type arguments can only be used in TypeScript files.
+index.js(9,12): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(13,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(19,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(23,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(27,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(28,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(32,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(39,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(43,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(47,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(48,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(52,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(53,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(59,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(63,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(67,11): error TS8010: Type annotations can only be used in TypeScript files.
+index.js(68,11): error TS8010: Type annotations can only be used in TypeScript files.
+
+
+==== index.js (21 errors) ====
+    // Pretty much all of this should be an error, (since index signatures and generics are forbidden in js),
+    // but we should be able to synthesize declarations from the symbols regardless
+    
+    export class M<T> {
+                   ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
+        field: T;
+               ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class N<U> extends M<U> {
+                   ~
+!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
+                                ~
+!!! error TS8011: Type arguments can only be used in TypeScript files.
+        other: U;
+               ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class O {
+        [idx: string]: string;
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class P extends O {}
+    
+    export class Q extends O {
+        [idx: string]: "ok";
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class R extends O {
+        [idx: number]: "ok";
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class S extends O {
+        [idx: string]: "ok";
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        [idx: number]: never;
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class T {
+        [idx: number]: string;
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class U extends T {}
+    
+    
+    export class V extends T {
+        [idx: string]: string;
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class W extends T {
+        [idx: number]: "ok";
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class X extends T {
+        [idx: string]: string;
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        [idx: number]: "ok";
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class Y {
+        [idx: string]: {x: number};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        [idx: number]: {x: number, y: number};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class Z extends Y {}
+    
+    export class AA extends Y {
+        [idx: string]: {x: number, y: number};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class BB extends Y {
+        [idx: number]: {x: 0, y: 0};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
+    export class CC extends Y {
+        [idx: string]: {x: number, y: number};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+        [idx: number]: {x: 0, y: 0};
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/jsDeclarationsEnums.errors.txt b/testdata/baselines/reference/submodule/conformance/jsDeclarationsEnums.errors.txt
new file mode 100644
index 0000000000..05318558dd
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/jsDeclarationsEnums.errors.txt
@@ -0,0 +1,101 @@
+index.js(4,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(6,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(10,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(14,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(18,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(22,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(24,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(30,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(35,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(41,19): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(47,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
+index.js(55,19): error TS8006: 'enum' declarations can only be used in TypeScript files.
+
+
+==== index.js (12 errors) ====
+    // Pretty much all of this should be an error, (since enums are forbidden in js),
+    // but we should be able to synthesize declarations from the symbols regardless
+    
+    export enum A {}
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+    
+    export enum B {
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        Member
+    }
+    
+    enum C {}
+         ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+    
+    export { C };
+    
+    enum DD {}
+         ~~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+    
+    export { DD as D };
+    
+    export enum E {}
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+    export { E as EE };
+    
+    export { F as FF };
+    export enum F {}
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+    
+    export enum G {
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        A = 1,
+        B,
+        C
+    }
+    
+    export enum H {
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        A = "a",
+        B = "b"
+    }
+    
+    export enum I {
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        A = "a",
+        B = 0,
+        C
+    }
+    
+    export const enum J {
+                      ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        A = 1,
+        B,
+        C
+    }
+    
+    export enum K {
+                ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        None   = 0,
+        A = 1 << 0,
+        B = 1 << 1,
+        C = 1 << 2,
+        Mask = A | B | C,
+    }
+    
+    export const enum L {
+                      ~
+!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
+        None   = 0,
+        A = 1 << 0,
+        B = 1 << 1,
+        C = 1 << 2,
+        Mask = A | B | C,
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/jsDeclarationsExportFormsErr.errors.txt b/testdata/baselines/reference/submodule/conformance/jsDeclarationsExportFormsErr.errors.txt
index 8bc742d706..b62dd98da9 100644
--- a/testdata/baselines/reference/submodule/conformance/jsDeclarationsExportFormsErr.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/jsDeclarationsExportFormsErr.errors.txt
@@ -1,12 +1,18 @@
+bar.js(1,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+bar.js(2,1): error TS8003: 'export =' can only be used in TypeScript files.
 globalNs.js(2,1): error TS1315: Global module exports may only appear in declaration files.
 
 
 ==== cls.js (0 errors) ====
     export class Foo {}
     
-==== bar.js (0 errors) ====
+==== bar.js (2 errors) ====
     import ns = require("./cls");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     export = ns; // TS Only
+    ~~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
     
 ==== bin.js (0 errors) ====
     import * as ns from "./cls";
diff --git a/testdata/baselines/reference/submodule/conformance/jsDeclarationsInterfaces.errors.txt b/testdata/baselines/reference/submodule/conformance/jsDeclarationsInterfaces.errors.txt
new file mode 100644
index 0000000000..2e672eb09b
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/jsDeclarationsInterfaces.errors.txt
@@ -0,0 +1,200 @@
+index.js(4,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(6,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(10,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(31,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(35,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(39,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(43,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(45,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(49,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(53,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(57,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(61,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(65,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(67,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(71,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(75,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(80,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(84,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(87,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(91,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(95,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(100,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(105,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(107,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(111,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+index.js(115,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+
+
+==== index.js (26 errors) ====
+    // Pretty much all of this should be an error, (since interfaces are forbidden in js),
+    // but we should be able to synthesize declarations from the symbols regardless
+    
+    export interface A {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export interface B {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        cat: string;
+    }
+    
+    export interface C<T, U> {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        field: T & U;
+        optionalField?: T;
+        readonly readonlyField: T & U;
+        readonly readonlyOptionalField?: U;
+        (): number;
+        (x: T): U;
+        <Q>(x: Q): T & Q;
+    
+        new (): string;
+        new (x: T): U;
+        new <Q>(x: Q): T & Q;
+    
+        method<Q = number>(): number;
+        method<Q>(a: T & Q): Q & number;
+        method(a?: number): number;
+        method(...args: any[]): number;
+    
+        optMethod?(): number;
+    }
+    
+    interface G {}
+              ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export { G };
+    
+    interface HH {}
+              ~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export { HH as H };
+    
+    export interface I {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    export { I as II };
+    
+    export { J as JJ };
+    export interface J {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export interface K extends I,J {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        x: string;
+    }
+    
+    export interface L extends K {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        y: string;
+    }
+    
+    export interface M<T> {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        field: T;
+    }
+    
+    export interface N<U> extends M<U> {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        other: U;
+    }
+    
+    export interface O {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: string;
+    }
+    
+    export interface P extends O {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export interface Q extends O {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: "ok";
+    }
+    
+    export interface R extends O {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: number]: "ok";
+    }
+    
+    export interface S extends O {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: "ok";
+        [idx: number]: never;
+    }
+    
+    export interface T {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: number]: string;
+    }
+    
+    export interface U extends T {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    
+    export interface V extends T {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: string;
+    }
+    
+    export interface W extends T {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: number]: "ok";
+    }
+    
+    export interface X extends T {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: string;
+        [idx: number]: "ok";
+    }
+    
+    export interface Y {
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: {x: number};
+        [idx: number]: {x: number, y: number};
+    }
+    
+    export interface Z extends Y {}
+                     ~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+    
+    export interface AA extends Y {
+                     ~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: {x: number, y: number};
+    }
+    
+    export interface BB extends Y {
+                     ~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: number]: {x: 0, y: 0};
+    }
+    
+    export interface CC extends Y {
+                     ~~
+!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+        [idx: string]: {x: number, y: number};
+        [idx: number]: {x: 0, y: 0};
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/jsDeclarationsTypeReferences4.errors.txt b/testdata/baselines/reference/submodule/conformance/jsDeclarationsTypeReferences4.errors.txt
new file mode 100644
index 0000000000..146844daa3
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/jsDeclarationsTypeReferences4.errors.txt
@@ -0,0 +1,23 @@
+index.js(4,18): error TS8006: 'namespace' declarations can only be used in TypeScript files.
+
+
+==== index.js (1 errors) ====
+    /// <reference types="node" />
+    export const Something = 2; // to show conflict that can occur
+    // @ts-ignore
+    export namespace A {
+                     ~
+!!! error TS8006: 'namespace' declarations can only be used in TypeScript files.
+        // @ts-ignore
+        export namespace B {
+            const Something = require("fs").Something;
+            const thing = new Something();
+            // @ts-ignore
+            export { thing };
+        }
+    }
+    
+==== node_modules/@types/node/index.d.ts (0 errors) ====
+    declare module "fs" {
+        export class Something {}
+    }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node16).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node16).errors.txt
index 7cbf2626ec..13ade2052e 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node16).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node16).errors.txt
@@ -9,10 +9,21 @@ index.cjs(16,22): error TS1479: The current file is a CommonJS module whose impo
 index.cjs(23,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another")' call instead.
 index.cjs(24,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/")' call instead.
 index.cjs(25,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/index")' call instead.
+index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(51,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(52,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(59,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(60,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(61,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -36,10 +47,21 @@ index.js(21,22): error TS2835: Relative import paths need explicit file extensio
 index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -63,10 +85,21 @@ index.mjs(21,22): error TS2835: Relative import paths need explicit file extensi
 index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -117,7 +150,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.js (27 errors) ====
+==== index.js (38 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -190,24 +223,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
@@ -259,7 +314,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.cjs (27 errors) ====
+==== index.cjs (38 errors) ====
     // ESM-format imports below should issue errors
     import * as m1 from "./index.js";
                         ~~~~~~~~~~~~
@@ -333,24 +388,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
@@ -402,7 +479,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // cjs format file
     const x = 1;
     export {x};
-==== index.mjs (27 errors) ====
+==== index.mjs (38 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -475,24 +552,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node18).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node18).errors.txt
index 7cbf2626ec..13ade2052e 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node18).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=node18).errors.txt
@@ -9,10 +9,21 @@ index.cjs(16,22): error TS1479: The current file is a CommonJS module whose impo
 index.cjs(23,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another")' call instead.
 index.cjs(24,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/")' call instead.
 index.cjs(25,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/index")' call instead.
+index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(51,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(52,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(59,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(60,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(61,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -36,10 +47,21 @@ index.js(21,22): error TS2835: Relative import paths need explicit file extensio
 index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -63,10 +85,21 @@ index.mjs(21,22): error TS2835: Relative import paths need explicit file extensi
 index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
 index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
@@ -117,7 +150,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.js (27 errors) ====
+==== index.js (38 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -190,24 +223,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
@@ -259,7 +314,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.cjs (27 errors) ====
+==== index.cjs (38 errors) ====
     // ESM-format imports below should issue errors
     import * as m1 from "./index.js";
                         ~~~~~~~~~~~~
@@ -333,24 +388,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
@@ -402,7 +479,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // cjs format file
     const x = 1;
     export {x};
-==== index.mjs (27 errors) ====
+==== index.mjs (38 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -475,24 +552,46 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~
 !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~
 !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     void m24;
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt
index f766eb28b5..ddbe7ecee4 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt
@@ -1,3 +1,14 @@
+index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
 index.cjs(77,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
@@ -20,6 +31,17 @@ index.js(21,22): error TS2835: Relative import paths need explicit file extensio
 index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
 index.js(76,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
@@ -42,6 +64,17 @@ index.mjs(21,22): error TS2835: Relative import paths need explicit file extensi
 index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
 index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
+index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
 index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
 index.mjs(76,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
@@ -91,7 +124,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.js (22 errors) ====
+==== index.js (33 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -164,16 +197,38 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     void m24;
     void m25;
     void m26;
@@ -223,7 +278,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // esm format file
     const x = 1;
     export {x};
-==== index.cjs (11 errors) ====
+==== index.cjs (22 errors) ====
     // ESM-format imports below should issue errors
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
@@ -275,16 +330,38 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     void m24;
     void m25;
     void m26;
@@ -334,7 +411,7 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     // cjs format file
     const x = 1;
     export {x};
-==== index.mjs (22 errors) ====
+==== index.mjs (33 errors) ====
     import * as m1 from "./index.js";
     import * as m2 from "./index.mjs";
     import * as m3 from "./index.cjs";
@@ -407,16 +484,38 @@ index.mjs(84,21): error TS2835: Relative import paths need explicit file extensi
     
     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
     import m24 = require("./");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m25 = require("./index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m26 = require("./subfolder");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m27 = require("./subfolder/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m28 = require("./subfolder/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m29 = require("./subfolder2");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m30 = require("./subfolder2/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m31 = require("./subfolder2/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m32 = require("./subfolder2/another");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m33 = require("./subfolder2/another/");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     import m34 = require("./subfolder2/another/index");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     void m24;
     void m25;
     void m26;
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt
index b80fa4321a..f3b7906029 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt
@@ -1,21 +1,27 @@
 file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
 index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
 
 
-==== subfolder/index.js (0 errors) ====
+==== subfolder/index.js (1 errors) ====
     // cjs format file
     const a = {};
     export = a;
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== subfolder/file.js (0 errors) ====
     // cjs format file
     const a = {};
     module.exports = a;
-==== index.js (1 errors) ====
+==== index.js (2 errors) ====
     // esm format file
     const a = {};
     export = a;
     ~~~~~~~~~~~
 !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== file.js (1 errors) ====
     // esm format file
     import "fs";
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt
index b80fa4321a..f3b7906029 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt
@@ -1,21 +1,27 @@
 file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
 index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
 
 
-==== subfolder/index.js (0 errors) ====
+==== subfolder/index.js (1 errors) ====
     // cjs format file
     const a = {};
     export = a;
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== subfolder/file.js (0 errors) ====
     // cjs format file
     const a = {};
     module.exports = a;
-==== index.js (1 errors) ====
+==== index.js (2 errors) ====
     // esm format file
     const a = {};
     export = a;
     ~~~~~~~~~~~
 !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== file.js (1 errors) ====
     // esm format file
     import "fs";
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt
index b80fa4321a..f3b7906029 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt
@@ -1,21 +1,27 @@
 file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
 index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
 
 
-==== subfolder/index.js (0 errors) ====
+==== subfolder/index.js (1 errors) ====
     // cjs format file
     const a = {};
     export = a;
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== subfolder/file.js (0 errors) ====
     // cjs format file
     const a = {};
     module.exports = a;
-==== index.js (1 errors) ====
+==== index.js (2 errors) ====
     // esm format file
     const a = {};
     export = a;
     ~~~~~~~~~~~
 !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+    ~~~~~~~~~~~
+!!! error TS8003: 'export =' can only be used in TypeScript files.
 ==== file.js (1 errors) ====
     // esm format file
     import "fs";
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt
new file mode 100644
index 0000000000..476c47f703
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt
@@ -0,0 +1,49 @@
+file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+
+
+==== subfolder/index.js (2 errors) ====
+    // cjs format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== index.js (2 errors) ====
+    // esm format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== file.js (2 errors) ====
+    // esm format file
+    const __require = null;
+    const _createRequire = null;
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== package.json (0 errors) ====
+    {
+        "name": "package",
+        "private": true,
+        "type": "module"
+    }
+==== subfolder/package.json (0 errors) ====
+    {
+        "type": "commonjs"
+    }
+==== types.d.ts (0 errors) ====
+    declare module "fs";
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt
new file mode 100644
index 0000000000..476c47f703
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt
@@ -0,0 +1,49 @@
+file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+
+
+==== subfolder/index.js (2 errors) ====
+    // cjs format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== index.js (2 errors) ====
+    // esm format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== file.js (2 errors) ====
+    // esm format file
+    const __require = null;
+    const _createRequire = null;
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== package.json (0 errors) ====
+    {
+        "name": "package",
+        "private": true,
+        "type": "module"
+    }
+==== subfolder/package.json (0 errors) ====
+    {
+        "type": "commonjs"
+    }
+==== types.d.ts (0 errors) ====
+    declare module "fs";
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt
new file mode 100644
index 0000000000..476c47f703
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt
@@ -0,0 +1,49 @@
+file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+
+
+==== subfolder/index.js (2 errors) ====
+    // cjs format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== index.js (2 errors) ====
+    // esm format file
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== file.js (2 errors) ====
+    // esm format file
+    const __require = null;
+    const _createRequire = null;
+    import fs = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    fs.readFile;
+    export import fs2 = require("fs");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+==== package.json (0 errors) ====
+    {
+        "name": "package",
+        "private": true,
+        "type": "module"
+    }
+==== subfolder/package.json (0 errors) ====
+    {
+        "type": "commonjs"
+    }
+==== types.d.ts (0 errors) ====
+    declare module "fs";
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt
index 4c4797fb6c..a4ba6ab81a 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt
@@ -1,33 +1,45 @@
+index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(3,22): error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 subfolder/index.js(2,17): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
+subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 subfolder/index.js(3,22): error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 
 
-==== subfolder/index.js (2 errors) ====
+==== subfolder/index.js (4 errors) ====
     // cjs format file
     import {h} from "../index.js";
                     ~~~~~~~~~~~~~
 !!! error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
 !!! error TS1479:   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
     import mod = require("../index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~
 !!! error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import {f as _f} from "./index.js";
     import mod2 = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     export async function f() {
         const mod3 = await import ("../index.js");
         const mod4 = await import ("./index.js");
         h();
     }
-==== index.js (1 errors) ====
+==== index.js (3 errors) ====
     // esm format file
     import {h as _h} from "./index.js";
     import mod = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~
 !!! error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import {f} from "./subfolder/index.js";
     import mod2 = require("./subfolder/index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     export async function h() {
         const mod3 = await import ("./index.js");
         const mod4 = await import ("./subfolder/index.js");
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt
index 4c4797fb6c..a4ba6ab81a 100644
--- a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt
@@ -1,33 +1,45 @@
+index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 index.js(3,22): error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 subfolder/index.js(2,17): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
+subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 subfolder/index.js(3,22): error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
+subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 
 
-==== subfolder/index.js (2 errors) ====
+==== subfolder/index.js (4 errors) ====
     // cjs format file
     import {h} from "../index.js";
                     ~~~~~~~~~~~~~
 !!! error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
 !!! error TS1479:   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
     import mod = require("../index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~~
 !!! error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import {f as _f} from "./index.js";
     import mod2 = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     export async function f() {
         const mod3 = await import ("../index.js");
         const mod4 = await import ("./index.js");
         h();
     }
-==== index.js (1 errors) ====
+==== index.js (3 errors) ====
     // esm format file
     import {h as _h} from "./index.js";
     import mod = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
                          ~~~~~~~~~~~~
 !!! error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
     import {f} from "./subfolder/index.js";
     import mod2 = require("./subfolder/index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
     export async function h() {
         const mod3 = await import ("./index.js");
         const mod4 = await import ("./subfolder/index.js");
diff --git a/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt
new file mode 100644
index 0000000000..2a46b9875d
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt
@@ -0,0 +1,46 @@
+index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+
+
+==== subfolder/index.js (2 errors) ====
+    // cjs format file
+    import {h} from "../index.js";
+    import mod = require("../index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    import {f as _f} from "./index.js";
+    import mod2 = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    export async function f() {
+        const mod3 = await import ("../index.js");
+        const mod4 = await import ("./index.js");
+        h();
+    }
+==== index.js (2 errors) ====
+    // esm format file
+    import {h as _h} from "./index.js";
+    import mod = require("./index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    import {f} from "./subfolder/index.js";
+    import mod2 = require("./subfolder/index.js");
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS8002: 'import ... =' can only be used in TypeScript files.
+    export async function h() {
+        const mod3 = await import ("./index.js");
+        const mod4 = await import ("./subfolder/index.js");
+        f();
+    }
+==== package.json (0 errors) ====
+    {
+        "name": "package",
+        "private": true,
+        "type": "module"
+    }
+==== subfolder/package.json (0 errors) ====
+    {
+        "type": "commonjs"
+    }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/override_js3.errors.txt b/testdata/baselines/reference/submodule/conformance/override_js3.errors.txt
new file mode 100644
index 0000000000..6e1d0dae65
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/override_js3.errors.txt
@@ -0,0 +1,17 @@
+a.js(7,5): error TS8009: The 'override' modifier can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    class B {
+        foo (v) {}
+        fooo (v) {}
+    }
+    
+    class D extends B {
+        override foo (v) {}
+        ~~~~~~~~
+!!! error TS8009: The 'override' modifier can only be used in TypeScript files.
+        /** @override */
+        fooo (v) {}
+    }
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression10.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression10.errors.txt
index 7982f84869..fca3c29810 100644
--- a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression10.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression10.errors.txt
@@ -1,5 +1,6 @@
 fileJs.js(1,1): error TS2304: Cannot find name 'a'.
 fileJs.js(1,11): error TS2304: Cannot find name 'c'.
+fileJs.js(1,11): error TS8010: Type annotations can only be used in TypeScript files.
 fileJs.js(1,17): error TS2304: Cannot find name 'd'.
 fileJs.js(1,27): error TS2304: Cannot find name 'f'.
 fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
@@ -8,12 +9,14 @@ fileTs.ts(1,17): error TS2304: Cannot find name 'd'.
 fileTs.ts(1,27): error TS2304: Cannot find name 'f'.
 
 
-==== fileJs.js (4 errors) ====
+==== fileJs.js (5 errors) ====
     a ? (b) : c => (d) : e => f // Not legal JS; "Unexpected token ':'" at last colon
     ~
 !!! error TS2304: Cannot find name 'a'.
               ~
 !!! error TS2304: Cannot find name 'c'.
+              ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
                     ~
 !!! error TS2304: Cannot find name 'd'.
                               ~
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression13.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression13.errors.txt
index fdda202361..cfe16ee6c8 100644
--- a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression13.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression13.errors.txt
@@ -1,15 +1,18 @@
 fileJs.js(1,1): error TS2304: Cannot find name 'a'.
 fileJs.js(1,11): error TS2304: Cannot find name 'a'.
+fileJs.js(1,21): error TS8010: Type annotations can only be used in TypeScript files.
 fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
 fileTs.ts(1,11): error TS2304: Cannot find name 'a'.
 
 
-==== fileJs.js (2 errors) ====
+==== fileJs.js (3 errors) ====
     a ? () => a() : (): any => null; // Not legal JS; "Unexpected token ')'" at last paren
     ~
 !!! error TS2304: Cannot find name 'a'.
               ~
 !!! error TS2304: Cannot find name 'a'.
+                        ~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
     
 ==== fileTs.ts (2 errors) ====
     a ? () => a() : (): any => null;
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression14.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression14.errors.txt
index a604d5e706..8908dde1bc 100644
--- a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression14.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression14.errors.txt
@@ -1,4 +1,8 @@
 fileJs.js(1,1): error TS2304: Cannot find name 'a'.
+fileJs.js(1,11): error TS8010: Type annotations can only be used in TypeScript files.
+fileJs.js(1,20): error TS8009: The '?' modifier can only be used in TypeScript files.
+fileJs.js(1,23): error TS8010: Type annotations can only be used in TypeScript files.
+fileJs.js(1,32): error TS8010: Type annotations can only be used in TypeScript files.
 fileJs.js(1,40): error TS2304: Cannot find name 'd'.
 fileJs.js(1,46): error TS2304: Cannot find name 'e'.
 fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
@@ -6,10 +10,18 @@ fileTs.ts(1,40): error TS2304: Cannot find name 'd'.
 fileTs.ts(1,46): error TS2304: Cannot find name 'e'.
 
 
-==== fileJs.js (3 errors) ====
+==== fileJs.js (7 errors) ====
     a() ? (b: number, c?: string): void => d() : e; // Not legal JS; "Unexpected token ':'" at first colon
     ~
 !!! error TS2304: Cannot find name 'a'.
+              ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+                       ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
+                          ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+                                   ~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
                                            ~
 !!! error TS2304: Cannot find name 'd'.
                                                  ~
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression15.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression15.errors.txt
new file mode 100644
index 0000000000..8cacfbe684
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression15.errors.txt
@@ -0,0 +1,11 @@
+fileJs.js(1,18): error TS8010: Type annotations can only be used in TypeScript files.
+
+
+==== fileJs.js (1 errors) ====
+    false ? (param): string => param : null // Not legal JS; "Unexpected token ':'" at last colon
+                     ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    
+==== fileTs.ts (0 errors) ====
+    false ? (param): string => param : null
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression16.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression16.errors.txt
new file mode 100644
index 0000000000..237f9839c1
--- /dev/null
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression16.errors.txt
@@ -0,0 +1,11 @@
+fileJs.js(1,25): error TS8010: Type annotations can only be used in TypeScript files.
+
+
+==== fileJs.js (1 errors) ====
+    true ? false ? (param): string => param : null : null // Not legal JS; "Unexpected token ':'" at last colon
+                            ~~~~~~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
+    
+==== fileTs.ts (0 errors) ====
+    true ? false ? (param): string => param : null : null
+    
\ No newline at end of file
diff --git a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression17.errors.txt b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression17.errors.txt
index 4d437b6b6c..28091b1745 100644
--- a/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression17.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/parserArrowFunctionExpression17.errors.txt
@@ -1,6 +1,7 @@
 fileJs.js(1,1): error TS2304: Cannot find name 'a'.
 fileJs.js(1,5): error TS2304: Cannot find name 'b'.
 fileJs.js(1,15): error TS2304: Cannot find name 'd'.
+fileJs.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
 fileJs.js(1,20): error TS2304: Cannot find name 'e'.
 fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
 fileTs.ts(1,5): error TS2304: Cannot find name 'b'.
@@ -8,7 +9,7 @@ fileTs.ts(1,15): error TS2304: Cannot find name 'd'.
 fileTs.ts(1,20): error TS2304: Cannot find name 'e'.
 
 
-==== fileJs.js (4 errors) ====
+==== fileJs.js (5 errors) ====
     a ? b : (c) : d => e // Not legal JS; "Unexpected token ':'" at last colon
     ~
 !!! error TS2304: Cannot find name 'a'.
@@ -16,6 +17,8 @@ fileTs.ts(1,20): error TS2304: Cannot find name 'e'.
 !!! error TS2304: Cannot find name 'b'.
                   ~
 !!! error TS2304: Cannot find name 'd'.
+                  ~
+!!! error TS8010: Type annotations can only be used in TypeScript files.
                        ~
 !!! error TS2304: Cannot find name 'e'.
     
diff --git a/testdata/baselines/reference/submodule/conformance/plainJSGrammarErrors.errors.txt b/testdata/baselines/reference/submodule/conformance/plainJSGrammarErrors.errors.txt
index 1b08565cd6..b92bd5df1b 100644
--- a/testdata/baselines/reference/submodule/conformance/plainJSGrammarErrors.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/plainJSGrammarErrors.errors.txt
@@ -5,11 +5,14 @@ plainJSGrammarErrors.js(14,13): error TS18038: 'for await' loops cannot be used
 plainJSGrammarErrors.js(17,9): error TS18041: A 'return' statement cannot be used inside a class static block.
 plainJSGrammarErrors.js(20,5): error TS1089: 'static' modifier cannot appear on a constructor declaration.
 plainJSGrammarErrors.js(21,5): error TS1089: 'async' modifier cannot appear on a constructor declaration.
+plainJSGrammarErrors.js(22,5): error TS8009: The 'const' modifier can only be used in TypeScript files.
 plainJSGrammarErrors.js(22,11): error TS1248: A class member cannot have the 'const' keyword.
+plainJSGrammarErrors.js(23,5): error TS8009: The 'const' modifier can only be used in TypeScript files.
 plainJSGrammarErrors.js(23,11): error TS1248: A class member cannot have the 'const' keyword.
 plainJSGrammarErrors.js(26,11): error TS1030: 'async' modifier already seen.
 plainJSGrammarErrors.js(28,11): error TS1029: 'static' modifier must precede 'async' modifier.
 plainJSGrammarErrors.js(29,5): error TS1031: 'export' modifier cannot appear on class elements of this kind.
+plainJSGrammarErrors.js(29,5): error TS8009: The 'export' modifier can only be used in TypeScript files.
 plainJSGrammarErrors.js(30,5): error TS1031: 'export' modifier cannot appear on class elements of this kind.
 plainJSGrammarErrors.js(34,22): error TS1005: '{' expected.
 plainJSGrammarErrors.js(35,9): error TS1054: A 'get' accessor cannot have parameters.
@@ -26,12 +29,16 @@ plainJSGrammarErrors.js(51,9): error TS18013: Property '#m' is not accessible ou
 plainJSGrammarErrors.js(54,8): error TS1030: 'export' modifier already seen.
 plainJSGrammarErrors.js(55,8): error TS1044: 'static' modifier cannot appear on a module or namespace element.
 plainJSGrammarErrors.js(56,22): error TS1090: 'static' modifier cannot appear on a parameter.
+plainJSGrammarErrors.js(56,22): error TS8012: Parameter modifiers can only be used in TypeScript files.
 plainJSGrammarErrors.js(57,7): error TS1029: 'export' modifier must precede 'async' modifier.
 plainJSGrammarErrors.js(58,26): error TS1090: 'export' modifier cannot appear on a parameter.
+plainJSGrammarErrors.js(58,26): error TS8012: Parameter modifiers can only be used in TypeScript files.
 plainJSGrammarErrors.js(59,25): error TS1090: 'async' modifier cannot appear on a parameter.
+plainJSGrammarErrors.js(59,25): error TS8012: Parameter modifiers can only be used in TypeScript files.
 plainJSGrammarErrors.js(60,7): error TS1030: 'async' modifier already seen.
 plainJSGrammarErrors.js(61,1): error TS1042: 'async' modifier cannot be used here.
 plainJSGrammarErrors.js(62,5): error TS1042: 'async' modifier cannot be used here.
+plainJSGrammarErrors.js(62,5): error TS8009: The 'async' modifier can only be used in TypeScript files.
 plainJSGrammarErrors.js(64,1): error TS1042: 'async' modifier cannot be used here.
 plainJSGrammarErrors.js(65,1): error TS1042: 'async' modifier cannot be used here.
 plainJSGrammarErrors.js(66,1): error TS1042: 'async' modifier cannot be used here.
@@ -60,6 +67,7 @@ plainJSGrammarErrors.js(105,5): error TS18016: Private identifiers are not allow
 plainJSGrammarErrors.js(106,5): error TS1042: 'export' modifier cannot be used here.
 plainJSGrammarErrors.js(108,25): error TS1162: An object member cannot be declared optional.
 plainJSGrammarErrors.js(109,6): error TS1162: An object member cannot be declared optional.
+plainJSGrammarErrors.js(109,6): error TS8009: The '?' modifier can only be used in TypeScript files.
 plainJSGrammarErrors.js(110,15): error TS1255: A definite assignment assertion '!' is not permitted in this context.
 plainJSGrammarErrors.js(111,19): error TS1255: A definite assignment assertion '!' is not permitted in this context.
 plainJSGrammarErrors.js(114,16): error TS1312: Did you mean to use a ':'? An '=' can only follow a property name when the containing object literal is part of a destructuring pattern.
@@ -94,7 +102,7 @@ plainJSGrammarErrors.js(204,30): message TS1450: Dynamic imports can only accept
 plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot be spread element.
 
 
-==== plainJSGrammarErrors.js (94 errors) ====
+==== plainJSGrammarErrors.js (102 errors) ====
     class C {
         // #private mistakes
         q = #unbound
@@ -131,9 +139,13 @@ plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot
         ~~~~~
 !!! error TS1089: 'async' modifier cannot appear on a constructor declaration.
         const x = 1
+        ~~~~~
+!!! error TS8009: The 'const' modifier can only be used in TypeScript files.
               ~
 !!! error TS1248: A class member cannot have the 'const' keyword.
         const y() {
+        ~~~~~
+!!! error TS8009: The 'const' modifier can only be used in TypeScript files.
               ~
 !!! error TS1248: A class member cannot have the 'const' keyword.
             return 12
@@ -148,6 +160,8 @@ plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot
         export cantExportProperty = 1
         ~~~~~~
 !!! error TS1031: 'export' modifier cannot appear on class elements of this kind.
+        ~~~~~~
+!!! error TS8009: The 'export' modifier can only be used in TypeScript files.
         export cantExportMethod() {
         ~~~~~~
 !!! error TS1031: 'export' modifier cannot appear on class elements of this kind.
@@ -207,15 +221,21 @@ plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot
     function staticParam(static x = 1) { return x }
                          ~~~~~~
 !!! error TS1090: 'static' modifier cannot appear on a parameter.
+                         ~~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
     async export function oorder(x = 1) { return x }
           ~~~~~~
 !!! error TS1029: 'export' modifier must precede 'async' modifier.
     function cantExportParam(export x = 1) { return x }
                              ~~~~~~
 !!! error TS1090: 'export' modifier cannot appear on a parameter.
+                             ~~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
     function cantAsyncParam(async x = 1) { return x }
                             ~~~~~
 !!! error TS1090: 'async' modifier cannot appear on a parameter.
+                            ~~~~~
+!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
     async async function extremelyAsync() {}
           ~~~~~
 !!! error TS1030: 'async' modifier already seen.
@@ -225,6 +245,8 @@ plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot
         async cantAsyncPropert = 1
         ~~~~~
 !!! error TS1042: 'async' modifier cannot be used here.
+        ~~~~~
+!!! error TS8009: The 'async' modifier can only be used in TypeScript files.
     }
     async const cantAsyncConst = 2
     ~~~~~
@@ -328,6 +350,8 @@ plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot
         m?() { return 12 },
          ~
 !!! error TS1162: An object member cannot be declared optional.
+         ~
+!!! error TS8009: The '?' modifier can only be used in TypeScript files.
         definitely!,
                   ~
 !!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
diff --git a/testdata/baselines/reference/submodule/conformance/typeSatisfaction_js.errors.txt b/testdata/baselines/reference/submodule/conformance/typeSatisfaction_js.errors.txt
index c7b421034d..20288daecd 100644
--- a/testdata/baselines/reference/submodule/conformance/typeSatisfaction_js.errors.txt
+++ b/testdata/baselines/reference/submodule/conformance/typeSatisfaction_js.errors.txt
@@ -1,11 +1,14 @@
 error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
+/src/a.js(1,29): error TS8037: Type satisfaction expressions can only be used in TypeScript files.
 
 
 !!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 !!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-==== /src/a.js (0 errors) ====
+==== /src/a.js (1 errors) ====
     var v = undefined satisfies 1;
+                                ~
+!!! error TS8037: Type satisfaction expressions can only be used in TypeScript files.
     
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/ambientPropertyDeclarationInJs.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/ambientPropertyDeclarationInJs.errors.txt.diff
deleted file mode 100644
index 188fc9829d..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/ambientPropertyDeclarationInJs.errors.txt.diff
+++ /dev/null
@@ -1,25 +0,0 @@
---- old.ambientPropertyDeclarationInJs.errors.txt
-+++ new.ambientPropertyDeclarationInJs.errors.txt
-@@= skipped -0, +0 lines =@@
- /test.js(3,9): error TS2322: Type '{}' is not assignable to type 'string'.
--/test.js(6,5): error TS8009: The 'declare' modifier can only be used in TypeScript files.
--/test.js(6,19): error TS8010: Type annotations can only be used in TypeScript files.
- /test.js(9,19): error TS2339: Property 'foo' does not exist on type 'string'.
-
-
--==== /test.js (4 errors) ====
-+==== /test.js (2 errors) ====
-     class Foo {
-         constructor() {
-             this.prop = {};
-@@= skipped -12, +10 lines =@@
-         }
-     
-         declare prop: string;
--        ~~~~~~~
--!!! error TS8009: The 'declare' modifier can only be used in TypeScript files.
--                      ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-     
-         method() {
-             this.prop.foo
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile.errors.txt.diff
deleted file mode 100644
index 01b25dd180..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile.errors.txt.diff
+++ /dev/null
@@ -1,16 +0,0 @@
---- old.decoratorInJsFile.errors.txt
-+++ new.decoratorInJsFile.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(3,12): error TS8010: Type annotations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    @SomeDecorator
--    class SomeClass {
--        foo(x: number) {
--               ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    
--        }
--    }
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile1.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile1.errors.txt.diff
deleted file mode 100644
index 349ad2c6c6..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/decoratorInJsFile1.errors.txt.diff
+++ /dev/null
@@ -1,16 +0,0 @@
---- old.decoratorInJsFile1.errors.txt
-+++ new.decoratorInJsFile1.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(3,12): error TS8010: Type annotations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    @SomeDecorator
--    class SomeClass {
--        foo(x: number) {
--               ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    
--        }
--    }
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt.diff
deleted file mode 100644
index 4c2ce91c3f..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/fillInMissingTypeArgsOnJSConstructCalls.errors.txt.diff
+++ /dev/null
@@ -1,48 +0,0 @@
---- old.fillInMissingTypeArgsOnJSConstructCalls.errors.txt
-+++ new.fillInMissingTypeArgsOnJSConstructCalls.errors.txt
-@@= skipped -0, +0 lines =@@
--BaseB.js(2,24): error TS8004: Type parameter declarations can only be used in TypeScript files.
- BaseB.js(2,25): error TS1005: ',' expected.
- BaseB.js(3,14): error TS2304: Cannot find name 'Class'.
--BaseB.js(3,14): error TS8010: Type annotations can only be used in TypeScript files.
- BaseB.js(4,25): error TS2304: Cannot find name 'Class'.
--BaseB.js(4,25): error TS8010: Type annotations can only be used in TypeScript files.
--SubB.js(3,41): error TS8011: Type arguments can only be used in TypeScript files.
-
-
- ==== BaseA.js (0 errors) ====
-@@= skipped -13, +9 lines =@@
-     import BaseA from './BaseA';
-     export default class SubA extends BaseA {
-     }
--==== BaseB.js (6 errors) ====
-+==== BaseB.js (3 errors) ====
-     import BaseA from './BaseA';
-     export default class B<T: BaseA> {
--                           ~~~~~~~~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
-                             ~
- !!! error TS1005: ',' expected.
-         _AClass: Class<T>;
-                  ~~~~~
- !!! error TS2304: Cannot find name 'Class'.
--                 ~~~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-         constructor(AClass: Class<T>) {
-                             ~~~~~
- !!! error TS2304: Cannot find name 'Class'.
--                            ~~~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-             this._AClass = AClass;
-         }
-     }
--==== SubB.js (1 errors) ====
-+==== SubB.js (0 errors) ====
-     import SubA from './SubA';
-     import BaseB from './BaseB';
-     export default class SubB extends BaseB<SubA> {
--                                            ~~~~
--!!! error TS8011: Type arguments can only be used in TypeScript files.
-         constructor() {
-             super(SubA);
-         }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAbstractModifier.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAbstractModifier.errors.txt.diff
deleted file mode 100644
index ceba0f9db3..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAbstractModifier.errors.txt.diff
+++ /dev/null
@@ -1,20 +0,0 @@
---- old.jsFileCompilationAbstractModifier.errors.txt
-+++ new.jsFileCompilationAbstractModifier.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,1): error TS8009: The 'abstract' modifier can only be used in TypeScript files.
--a.js(2,5): error TS8009: The 'abstract' modifier can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (2 errors) ====
-+==== a.js (0 errors) ====
-     abstract class c {
--    ~~~~~~~~
--!!! error TS8009: The 'abstract' modifier can only be used in TypeScript files.
-         abstract x;
--        ~~~~~~~~
--!!! error TS8009: The 'abstract' modifier can only be used in TypeScript files.
-     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt.diff
deleted file mode 100644
index b6b3c82d97..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationAmbientVarDeclarationSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationAmbientVarDeclarationSyntax.errors.txt
-+++ new.jsFileCompilationAmbientVarDeclarationSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,1): error TS8009: The 'declare' modifier can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     declare var v;
--    ~~~~~~~
--!!! error TS8009: The 'declare' modifier can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt.diff
deleted file mode 100644
index 6c10af799b..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationConstructorOverloadSyntax.errors.txt.diff
+++ /dev/null
@@ -1,14 +0,0 @@
---- old.jsFileCompilationConstructorOverloadSyntax.errors.txt
-+++ new.jsFileCompilationConstructorOverloadSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    class A {
--      constructor();
--      ~~~~~~~~~~~
--!!! error TS8017: Signature declarations can only be used in TypeScript files.
--    }
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationEnumSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationEnumSyntax.errors.txt.diff
deleted file mode 100644
index 216b463d40..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationEnumSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationEnumSyntax.errors.txt
-+++ new.jsFileCompilationEnumSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     enum E { }
--         ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt.diff
deleted file mode 100644
index 530f0d0ab4..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationExportAssignmentSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationExportAssignmentSyntax.errors.txt
-+++ new.jsFileCompilationExportAssignmentSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,1): error TS8003: 'export =' can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     export = b;
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt.diff
deleted file mode 100644
index 0251a5ce1e..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationFunctionOverloadSyntax.errors.txt.diff
+++ /dev/null
@@ -1,12 +0,0 @@
---- old.jsFileCompilationFunctionOverloadSyntax.errors.txt
-+++ new.jsFileCompilationFunctionOverloadSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(1,10): error TS8017: Signature declarations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    function foo();
--             ~~~
--!!! error TS8017: Signature declarations can only be used in TypeScript files.
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt.diff
deleted file mode 100644
index a710e3349d..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt
-+++ new.jsFileCompilationHeritageClauseSyntaxOfClass.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,9): error TS8005: 'implements' clauses can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     class C implements D { }
--            ~~~~~~~~~~~~
--!!! error TS8005: 'implements' clauses can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationImportEqualsSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationImportEqualsSyntax.errors.txt.diff
deleted file mode 100644
index 36f4f35e3f..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationImportEqualsSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationImportEqualsSyntax.errors.txt
-+++ new.jsFileCompilationImportEqualsSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,1): error TS8002: 'import ... =' can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     import a = b;
--    ~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationInterfaceSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationInterfaceSyntax.errors.txt.diff
deleted file mode 100644
index b7090eb786..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationInterfaceSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationInterfaceSyntax.errors.txt
-+++ new.jsFileCompilationInterfaceSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     interface I { }
--              ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt.diff
deleted file mode 100644
index f7e96404d2..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationMethodOverloadSyntax.errors.txt.diff
+++ /dev/null
@@ -1,14 +0,0 @@
---- old.jsFileCompilationMethodOverloadSyntax.errors.txt
-+++ new.jsFileCompilationMethodOverloadSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    class A {
--      foo();
--      ~~~
--!!! error TS8017: Signature declarations can only be used in TypeScript files.
--    }
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationModuleSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationModuleSyntax.errors.txt.diff
deleted file mode 100644
index fea4d1f2ef..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationModuleSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationModuleSyntax.errors.txt
-+++ new.jsFileCompilationModuleSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,8): error TS8006: 'module' declarations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     module M { }
--           ~
--!!! error TS8006: 'module' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationNonNullAssertion.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationNonNullAssertion.errors.txt.diff
index 5599398c6c..774688f7f7 100644
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationNonNullAssertion.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationNonNullAssertion.errors.txt.diff
@@ -1,20 +1,15 @@
 --- old.jsFileCompilationNonNullAssertion.errors.txt
 +++ new.jsFileCompilationNonNullAssertion.errors.txt
 @@= skipped -0, +0 lines =@@
--/src/a.js(1,1): error TS8013: Non-null assertions can only be used in TypeScript files.
--
--
--==== /src/a.js (1 errors) ====
 +error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-+
-+
+ /src/a.js(1,1): error TS8013: Non-null assertions can only be used in TypeScript files.
+
+
 +!!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +!!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-+==== /src/a.js (0 errors) ====
+ ==== /src/a.js (1 errors) ====
      0!
--    ~~
--!!! error TS8013: Non-null assertions can only be used in TypeScript files.
-     
\ No newline at end of file
+     ~~
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt.diff
deleted file mode 100644
index 7a2b34613c..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt.diff
+++ /dev/null
@@ -1,22 +0,0 @@
---- old.jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt
-+++ new.jsFileCompilationOptionalClassElementSyntaxOfClass.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(2,8): error TS8009: The '?' modifier can only be used in TypeScript files.
--a.js(4,8): error TS8009: The '?' modifier can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (2 errors) ====
-+==== a.js (0 errors) ====
-     class C {
-         foo?() {
--           ~
--!!! error TS8009: The '?' modifier can only be used in TypeScript files.
-         }
-         bar? = 1; 
--           ~
--!!! error TS8009: The '?' modifier can only be used in TypeScript files.
-     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalParameter.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalParameter.errors.txt.diff
deleted file mode 100644
index 1449369838..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationOptionalParameter.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationOptionalParameter.errors.txt
-+++ new.jsFileCompilationOptionalParameter.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,13): error TS8009: The '?' modifier can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     function F(p?) { }
--                ~
--!!! error TS8009: The '?' modifier can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt.diff
deleted file mode 100644
index 7b12a213e1..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicMethodSyntaxOfClass.errors.txt.diff
+++ /dev/null
@@ -1,18 +0,0 @@
---- old.jsFileCompilationPublicMethodSyntaxOfClass.errors.txt
-+++ new.jsFileCompilationPublicMethodSyntaxOfClass.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(2,5): error TS8009: The 'public' modifier can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     class C {
-         public foo() {
--        ~~~~~~
--!!! error TS8009: The 'public' modifier can only be used in TypeScript files.
-         }
-     }
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicParameterModifier.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicParameterModifier.errors.txt.diff
deleted file mode 100644
index 9563e07b1a..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationPublicParameterModifier.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationPublicParameterModifier.errors.txt
-+++ new.jsFileCompilationPublicParameterModifier.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,23): error TS8012: Parameter modifiers can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     class C { constructor(public x) { }}
--                          ~~~~~~
--!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt.diff
deleted file mode 100644
index 2fbcaadba2..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt
-+++ new.jsFileCompilationReturnTypeSyntaxOfFunction.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     function F(): number { }
--                  ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAliasSyntax.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAliasSyntax.errors.txt.diff
deleted file mode 100644
index c78a471eb3..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAliasSyntax.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationTypeAliasSyntax.errors.txt
-+++ new.jsFileCompilationTypeAliasSyntax.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,6): error TS8008: Type aliases can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     type a = b;
--         ~
--!!! error TS8008: Type aliases can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAssertions.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAssertions.errors.txt.diff
index 89dc3ac954..c859e79ebe 100644
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAssertions.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeAssertions.errors.txt.diff
@@ -1,22 +1,17 @@
 --- old.jsFileCompilationTypeAssertions.errors.txt
 +++ new.jsFileCompilationTypeAssertions.errors.txt
 @@= skipped -0, +0 lines =@@
--/src/a.js(1,6): error TS8016: Type assertion expressions can only be used in TypeScript files.
 +error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
+ /src/a.js(1,6): error TS8016: Type assertion expressions can only be used in TypeScript files.
  /src/a.js(2,10): error TS17008: JSX element 'string' has no corresponding closing tag.
  /src/a.js(3,1): error TS1005: '</' expected.
 
 
--==== /src/a.js (3 errors) ====
 +!!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +!!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-+==== /src/a.js (2 errors) ====
+ ==== /src/a.js (3 errors) ====
      0 as number;
--         ~~~~~~
--!!! error TS8016: Type assertion expressions can only be used in TypeScript files.
-     var v = <string>undefined;
-              ~~~~~~
- !!! error TS17008: JSX element 'string' has no corresponding closing tag.
\ No newline at end of file
+          ~~~~~~
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeOfParameter.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeOfParameter.errors.txt.diff
deleted file mode 100644
index caf9b849dc..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeOfParameter.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationTypeOfParameter.errors.txt
-+++ new.jsFileCompilationTypeOfParameter.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     function F(a: number) { }
--                  ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt.diff
deleted file mode 100644
index cf5851e510..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClass.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationTypeParameterSyntaxOfClass.errors.txt
-+++ new.jsFileCompilationTypeParameterSyntaxOfClass.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,9): error TS8004: Type parameter declarations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     class C<T> { }
--            ~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt.diff
deleted file mode 100644
index eeb9c0f857..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt.diff
+++ /dev/null
@@ -1,12 +0,0 @@
---- old.jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt
-+++ new.jsFileCompilationTypeParameterSyntaxOfClassExpression.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(1,19): error TS8004: Type parameter declarations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    const Bar = class<T> {};
--                      ~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt.diff
deleted file mode 100644
index ccebf9c041..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt
-+++ new.jsFileCompilationTypeParameterSyntaxOfFunction.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,12): error TS8004: Type parameter declarations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     function F<T>() { }
--               ~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt.diff
deleted file mode 100644
index eb1c29ba40..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsFileCompilationTypeSyntaxOfVar.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.jsFileCompilationTypeSyntaxOfVar.errors.txt
-+++ new.jsFileCompilationTypeSyntaxOfVar.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file 'a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--a.js(1,8): error TS8010: Type annotations can only be used in TypeScript files.
-
-
- !!! error TS5055: Cannot write file 'a.js' because it would overwrite input file.
- !!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
--==== a.js (1 errors) ====
-+==== a.js (0 errors) ====
-     var v: () => number;
--           ~~~~~~~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/jsdocTypedefNoCrash2.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/jsdocTypedefNoCrash2.errors.txt.diff
index 4d78ec0273..294da8e1b7 100644
--- a/testdata/baselines/reference/submoduleAccepted/compiler/jsdocTypedefNoCrash2.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/compiler/jsdocTypedefNoCrash2.errors.txt.diff
@@ -2,21 +2,23 @@
 +++ new.jsdocTypedefNoCrash2.errors.txt
 @@= skipped -0, +0 lines =@@
 -export.js(1,13): error TS2451: Cannot redeclare block-scoped variable 'foo'.
--export.js(1,13): error TS8008: Type aliases can only be used in TypeScript files.
+ export.js(1,13): error TS8008: Type aliases can only be used in TypeScript files.
 -export.js(6,14): error TS2451: Cannot redeclare block-scoped variable 'foo'.
 -
 -
 -==== export.js (3 errors) ====
--    export type foo = 5;
--                ~~~
++
++
++==== export.js (1 errors) ====
+     export type foo = 5;
+                 ~~~
 -!!! error TS2451: Cannot redeclare block-scoped variable 'foo'.
 -                ~~~
--!!! error TS8008: Type aliases can only be used in TypeScript files.
--    /**
--     * @typedef {{
--     * }}
--     */
--    export const foo = 5;
+ !!! error TS8008: Type aliases can only be used in TypeScript files.
+     /**
+      * @typedef {{
+      * }}
+      */
+     export const foo = 5;
 -                 ~~~
--!!! error TS2451: Cannot redeclare block-scoped variable 'foo'.
-+<no content>
\ No newline at end of file
+-!!! error TS2451: Cannot redeclare block-scoped variable 'foo'.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/modulePreserve4.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/modulePreserve4.errors.txt.diff
index 85fd403b08..344e42e5be 100644
--- a/testdata/baselines/reference/submoduleAccepted/compiler/modulePreserve4.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/compiler/modulePreserve4.errors.txt.diff
@@ -14,12 +14,11 @@
  /main2.mts(14,8): error TS1192: Module '"/e"' has no default export.
  /main3.cjs(1,10): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
 -/main3.cjs(1,13): error TS2305: Module '"./a"' has no exported member 'y'.
--/main3.cjs(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
 +/main3.cjs(1,13): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
+ /main3.cjs(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
  /main3.cjs(5,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
  /main3.cjs(8,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
- /main3.cjs(10,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
-@@= skipped -18, +15 lines =@@
+@@= skipped -18, +16 lines =@@
  /main3.cjs(17,8): error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
 
 
@@ -58,21 +57,12 @@
      import a1 = require("./a"); // { x: 0 }
      a1.x;
      a1.default.x; // Arguably should exist but doesn't
-@@= skipped -33, +33 lines =@@
-     import g1 from "./g"; // { default: 0 }
-     import g2 = require("./g"); // { default: 0 }
-     
--==== /main3.cjs (9 errors) ====
-+==== /main3.cjs (8 errors) ====
-     import { x, y } from "./a"; // No y
+@@= skipped -38, +38 lines =@@
               ~
  !!! error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
                  ~
 -!!! error TS2305: Module '"./a"' has no exported member 'y'.
 +!!! error TS1293: ESM syntax is not allowed in a CommonJS module when 'module' is set to 'preserve'.
      import a1 = require("./a"); // Error in JS
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     const a2 = require("./a"); // { x: 0 }
-     
-     import b1 from "./b"; // 0
\ No newline at end of file
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ !!! error TS8002: 'import ... =' can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt.diff
deleted file mode 100644
index 4989352fd0..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/compiler/thisAssignmentInNamespaceDeclaration1.errors.txt.diff
+++ /dev/null
@@ -1,27 +0,0 @@
---- old.thisAssignmentInNamespaceDeclaration1.errors.txt
-+++ new.thisAssignmentInNamespaceDeclaration1.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(1,8): error TS8006: 'module' declarations can only be used in TypeScript files.
- a.js(2,5): error TS2331: 'this' cannot be referenced in a module or namespace body.
--b.js(1,11): error TS8006: 'namespace' declarations can only be used in TypeScript files.
- b.js(2,5): error TS2331: 'this' cannot be referenced in a module or namespace body.
-
-
--==== a.js (2 errors) ====
-+==== a.js (1 errors) ====
-     module foo {
--           ~~~
--!!! error TS8006: 'module' declarations can only be used in TypeScript files.
-         this.bar = 4;
-         ~~~~
- !!! error TS2331: 'this' cannot be referenced in a module or namespace body.
-     }
-     
--==== b.js (2 errors) ====
-+==== b.js (1 errors) ====
-     namespace blah {
--              ~~~~
--!!! error TS8006: 'namespace' declarations can only be used in TypeScript files.
-         this.prop = 42;
-         ~~~~
- !!! error TS2331: 'this' cannot be referenced in a module or namespace body.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/exportNamespace_js.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/exportNamespace_js.errors.txt.diff
deleted file mode 100644
index db304cbfa3..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/exportNamespace_js.errors.txt.diff
+++ /dev/null
@@ -1,18 +0,0 @@
---- old.exportNamespace_js.errors.txt
-+++ new.exportNamespace_js.errors.txt
-@@= skipped -0, +0 lines =@@
--b.js(1,1): error TS8006: 'export type' declarations can only be used in TypeScript files.
- c.js(2,1): error TS1362: 'A' cannot be used as a value because it was exported using 'export type'.
-
-
- ==== a.js (0 errors) ====
-     export class A {}
-     
--==== b.js (1 errors) ====
-+==== b.js (0 errors) ====
-     export type * from './a';
--    ~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8006: 'export type' declarations can only be used in TypeScript files.
-     
- ==== c.js (1 errors) ====
-     import { A } from './b';
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/exportSpecifiers_js.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/exportSpecifiers_js.errors.txt.diff
deleted file mode 100644
index 51f38d66e6..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/exportSpecifiers_js.errors.txt.diff
+++ /dev/null
@@ -1,13 +0,0 @@
---- old.exportSpecifiers_js.errors.txt
-+++ new.exportSpecifiers_js.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(2,10): error TS8006: 'export...type' declarations can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    const foo = 0;
--    export { type foo };
--             ~~~~~~~~
--!!! error TS8006: 'export...type' declarations can only be used in TypeScript files.
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/grammarErrors.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/grammarErrors.errors.txt.diff
deleted file mode 100644
index 30becf83db..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/grammarErrors.errors.txt.diff
+++ /dev/null
@@ -1,26 +0,0 @@
---- old.grammarErrors.errors.txt
-+++ new.grammarErrors.errors.txt
-@@= skipped -0, +0 lines =@@
- error TS5055: Cannot write file '/a.js' because it would overwrite input file.
-   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
- error TS5056: Cannot write file '/a.js' because it would be overwritten by multiple input files.
--/a.js(1,1): error TS8006: 'import type' declarations can only be used in TypeScript files.
--/a.js(2,1): error TS8006: 'export type' declarations can only be used in TypeScript files.
- /b.ts(1,8): error TS1363: A type-only import can specify a default import or named bindings, but not both.
- /c.ts(4,1): error TS1392: An import alias cannot use 'import type'
-
-@@= skipped -19, +17 lines =@@
-            ~~~~~~~~~~~~~~~~
- !!! error TS1363: A type-only import can specify a default import or named bindings, but not both.
-     
--==== /a.js (2 errors) ====
-+==== /a.js (0 errors) ====
-     import type A from './a';
--    ~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8006: 'import type' declarations can only be used in TypeScript files.
-     export type { A };
--    ~~~~~~~~~~~~~~~~~~
--!!! error TS8006: 'export type' declarations can only be used in TypeScript files.
-     
- ==== /c.ts (1 errors) ====
-     namespace ns {
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/importSpecifiers_js.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/importSpecifiers_js.errors.txt.diff
deleted file mode 100644
index 13191d59af..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/importSpecifiers_js.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.importSpecifiers_js.errors.txt
-+++ new.importSpecifiers_js.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(1,10): error TS8006: 'import...type' declarations can only be used in TypeScript files.
--
--
--==== a.ts (0 errors) ====
--    export interface A {}
--    
--==== a.js (1 errors) ====
--    import { type A } from "./a";
--             ~~~~~~
--!!! error TS8006: 'import...type' declarations can only be used in TypeScript files.
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsClassesErr.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsClassesErr.errors.txt.diff
deleted file mode 100644
index 9ae89ec417..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsClassesErr.errors.txt.diff
+++ /dev/null
@@ -1,140 +0,0 @@
---- old.jsDeclarationsClassesErr.errors.txt
-+++ new.jsDeclarationsClassesErr.errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(4,16): error TS8004: Type parameter declarations can only be used in TypeScript files.
--index.js(5,12): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(8,16): error TS8004: Type parameter declarations can only be used in TypeScript files.
--index.js(8,29): error TS8011: Type arguments can only be used in TypeScript files.
--index.js(9,12): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(13,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(19,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(23,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(27,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(28,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(32,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(39,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(43,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(47,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(48,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(52,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(53,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(59,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(63,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(67,11): error TS8010: Type annotations can only be used in TypeScript files.
--index.js(68,11): error TS8010: Type annotations can only be used in TypeScript files.
--
--
--==== index.js (21 errors) ====
--    // Pretty much all of this should be an error, (since index signatures and generics are forbidden in js),
--    // but we should be able to synthesize declarations from the symbols regardless
--    
--    export class M<T> {
--                   ~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
--        field: T;
--               ~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class N<U> extends M<U> {
--                   ~
--!!! error TS8004: Type parameter declarations can only be used in TypeScript files.
--                                ~
--!!! error TS8011: Type arguments can only be used in TypeScript files.
--        other: U;
--               ~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class O {
--        [idx: string]: string;
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class P extends O {}
--    
--    export class Q extends O {
--        [idx: string]: "ok";
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class R extends O {
--        [idx: number]: "ok";
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class S extends O {
--        [idx: string]: "ok";
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--        [idx: number]: never;
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class T {
--        [idx: number]: string;
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class U extends T {}
--    
--    
--    export class V extends T {
--        [idx: string]: string;
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class W extends T {
--        [idx: number]: "ok";
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class X extends T {
--        [idx: string]: string;
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--        [idx: number]: "ok";
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class Y {
--        [idx: string]: {x: number};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--        [idx: number]: {x: number, y: number};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class Z extends Y {}
--    
--    export class AA extends Y {
--        [idx: string]: {x: number, y: number};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class BB extends Y {
--        [idx: number]: {x: 0, y: 0};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
--    export class CC extends Y {
--        [idx: string]: {x: number, y: number};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--        [idx: number]: {x: 0, y: 0};
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    }
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsEnums.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsEnums.errors.txt.diff
deleted file mode 100644
index e00f7c667e..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsEnums.errors.txt.diff
+++ /dev/null
@@ -1,105 +0,0 @@
---- old.jsDeclarationsEnums.errors.txt
-+++ new.jsDeclarationsEnums.errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(4,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(6,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(10,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(14,6): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(18,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(22,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(24,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(30,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(35,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(41,19): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(47,13): error TS8006: 'enum' declarations can only be used in TypeScript files.
--index.js(55,19): error TS8006: 'enum' declarations can only be used in TypeScript files.
--
--
--==== index.js (12 errors) ====
--    // Pretty much all of this should be an error, (since enums are forbidden in js),
--    // but we should be able to synthesize declarations from the symbols regardless
--    
--    export enum A {}
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--    
--    export enum B {
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        Member
--    }
--    
--    enum C {}
--         ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--    
--    export { C };
--    
--    enum DD {}
--         ~~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--    
--    export { DD as D };
--    
--    export enum E {}
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--    export { E as EE };
--    
--    export { F as FF };
--    export enum F {}
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--    
--    export enum G {
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        A = 1,
--        B,
--        C
--    }
--    
--    export enum H {
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        A = "a",
--        B = "b"
--    }
--    
--    export enum I {
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        A = "a",
--        B = 0,
--        C
--    }
--    
--    export const enum J {
--                      ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        A = 1,
--        B,
--        C
--    }
--    
--    export enum K {
--                ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        None   = 0,
--        A = 1 << 0,
--        B = 1 << 1,
--        C = 1 << 2,
--        Mask = A | B | C,
--    }
--    
--    export const enum L {
--                      ~
--!!! error TS8006: 'enum' declarations can only be used in TypeScript files.
--        None   = 0,
--        A = 1 << 0,
--        B = 1 << 1,
--        C = 1 << 2,
--        Mask = A | B | C,
--    }
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsExportFormsErr.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsExportFormsErr.errors.txt.diff
index fad73826d0..d387876f66 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsExportFormsErr.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsExportFormsErr.errors.txt.diff
@@ -1,23 +1,15 @@
 --- old.jsDeclarationsExportFormsErr.errors.txt
 +++ new.jsDeclarationsExportFormsErr.errors.txt
 @@= skipped -0, +0 lines =@@
--bar.js(1,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--bar.js(2,1): error TS8003: 'export =' can only be used in TypeScript files.
+ bar.js(1,1): error TS8002: 'import ... =' can only be used in TypeScript files.
+ bar.js(2,1): error TS8003: 'export =' can only be used in TypeScript files.
 -bin.js(2,1): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
  globalNs.js(2,1): error TS1315: Global module exports may only appear in declaration files.
 
 
- ==== cls.js (0 errors) ====
-     export class Foo {}
-     
--==== bar.js (2 errors) ====
-+==== bar.js (0 errors) ====
-     import ns = require("./cls");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     export = ns; // TS Only
--    ~~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
+@@= skipped -14, +13 lines =@@
+     ~~~~~~~~~~~~
+ !!! error TS8003: 'export =' can only be used in TypeScript files.
      
 -==== bin.js (1 errors) ====
 +==== bin.js (0 errors) ====
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsInterfaces.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsInterfaces.errors.txt.diff
index 604789c684..d8f703a957 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsInterfaces.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsInterfaces.errors.txt.diff
@@ -1,216 +1,52 @@
 --- old.jsDeclarationsInterfaces.errors.txt
 +++ new.jsDeclarationsInterfaces.errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(4,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(6,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(10,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(31,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+@@= skipped -1, +1 lines =@@
+ index.js(6,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(10,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(31,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
 -index.js(33,10): error TS18043: Types cannot appear in export declarations in JavaScript files.
--index.js(35,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(35,11): error TS8006: 'interface' declarations can only be used in TypeScript files.
 -index.js(37,10): error TS18043: Types cannot appear in export declarations in JavaScript files.
--index.js(39,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(39,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
 -index.js(40,10): error TS18043: Types cannot appear in export declarations in JavaScript files.
 -index.js(42,10): error TS18043: Types cannot appear in export declarations in JavaScript files.
--index.js(43,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(45,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(49,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(53,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(57,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(61,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(65,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(67,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(71,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(75,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(80,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(84,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(87,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(91,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(95,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(100,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(105,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(107,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(111,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--index.js(115,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
--
--
+ index.js(43,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(45,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+ index.js(49,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+@@= skipped -28, +24 lines =@@
+ index.js(115,18): error TS8006: 'interface' declarations can only be used in TypeScript files.
+
+
 -==== index.js (30 errors) ====
--    // Pretty much all of this should be an error, (since interfaces are forbidden in js),
--    // but we should be able to synthesize declarations from the symbols regardless
--    
--    export interface A {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export interface B {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        cat: string;
--    }
--    
--    export interface C<T, U> {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        field: T & U;
--        optionalField?: T;
--        readonly readonlyField: T & U;
--        readonly readonlyOptionalField?: U;
--        (): number;
--        (x: T): U;
--        <Q>(x: Q): T & Q;
--    
--        new (): string;
--        new (x: T): U;
--        new <Q>(x: Q): T & Q;
--    
--        method<Q = number>(): number;
--        method<Q>(a: T & Q): Q & number;
--        method(a?: number): number;
--        method(...args: any[]): number;
--    
--        optMethod?(): number;
--    }
--    
--    interface G {}
--              ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export { G };
++==== index.js (26 errors) ====
+     // Pretty much all of this should be an error, (since interfaces are forbidden in js),
+     // but we should be able to synthesize declarations from the symbols regardless
+     
+@@= skipped -42, +42 lines =@@
+ !!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+     
+     export { G };
 -             ~
 -!!! error TS18043: Types cannot appear in export declarations in JavaScript files.
--    
--    interface HH {}
--              ~~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export { HH as H };
+     
+     interface HH {}
+               ~~
+ !!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+     
+     export { HH as H };
 -             ~~
 -!!! error TS18043: Types cannot appear in export declarations in JavaScript files.
--    
--    export interface I {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    export { I as II };
+     
+     export interface I {}
+                      ~
+ !!! error TS8006: 'interface' declarations can only be used in TypeScript files.
+     export { I as II };
 -             ~
 -!!! error TS18043: Types cannot appear in export declarations in JavaScript files.
--    
--    export { J as JJ };
+     
+     export { J as JJ };
 -             ~
 -!!! error TS18043: Types cannot appear in export declarations in JavaScript files.
--    export interface J {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export interface K extends I,J {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        x: string;
--    }
--    
--    export interface L extends K {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        y: string;
--    }
--    
--    export interface M<T> {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        field: T;
--    }
--    
--    export interface N<U> extends M<U> {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        other: U;
--    }
--    
--    export interface O {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: string;
--    }
--    
--    export interface P extends O {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export interface Q extends O {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: "ok";
--    }
--    
--    export interface R extends O {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: number]: "ok";
--    }
--    
--    export interface S extends O {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: "ok";
--        [idx: number]: never;
--    }
--    
--    export interface T {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: number]: string;
--    }
--    
--    export interface U extends T {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    
--    export interface V extends T {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: string;
--    }
--    
--    export interface W extends T {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: number]: "ok";
--    }
--    
--    export interface X extends T {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: string;
--        [idx: number]: "ok";
--    }
--    
--    export interface Y {
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: {x: number};
--        [idx: number]: {x: number, y: number};
--    }
--    
--    export interface Z extends Y {}
--                     ~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--    
--    export interface AA extends Y {
--                     ~~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: {x: number, y: number};
--    }
--    
--    export interface BB extends Y {
--                     ~~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: number]: {x: 0, y: 0};
--    }
--    
--    export interface CC extends Y {
--                     ~~
--!!! error TS8006: 'interface' declarations can only be used in TypeScript files.
--        [idx: string]: {x: number, y: number};
--        [idx: number]: {x: 0, y: 0};
--    }
--    
-+<no content>
\ No newline at end of file
+     export interface J {}
+                      ~
+ !!! error TS8006: 'interface' declarations can only be used in TypeScript files.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsTypeReferences4.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsTypeReferences4.errors.txt.diff
deleted file mode 100644
index a75e868ac2..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/jsDeclarationsTypeReferences4.errors.txt.diff
+++ /dev/null
@@ -1,27 +0,0 @@
---- old.jsDeclarationsTypeReferences4.errors.txt
-+++ new.jsDeclarationsTypeReferences4.errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(4,18): error TS8006: 'namespace' declarations can only be used in TypeScript files.
--
--
--==== index.js (1 errors) ====
--    /// <reference types="node" />
--    export const Something = 2; // to show conflict that can occur
--    // @ts-ignore
--    export namespace A {
--                     ~
--!!! error TS8006: 'namespace' declarations can only be used in TypeScript files.
--        // @ts-ignore
--        export namespace B {
--            const Something = require("fs").Something;
--            const thing = new Something();
--            // @ts-ignore
--            export { thing };
--        }
--    }
--    
--==== node_modules/@types/node/index.d.ts (0 errors) ====
--    declare module "fs" {
--        export class Something {}
--    }
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node16).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node16).errors.txt.diff
deleted file mode 100644
index e443064e79..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node16).errors.txt.diff
+++ /dev/null
@@ -1,236 +0,0 @@
---- old.nodeModulesAllowJs1(module=node16).errors.txt
-+++ new.nodeModulesAllowJs1(module=node16).errors.txt
-@@= skipped -8, +8 lines =@@
- index.cjs(23,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another")' call instead.
- index.cjs(24,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/")' call instead.
- index.cjs(25,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/index")' call instead.
--index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(51,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(52,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(59,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(60,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(61,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -38, +27 lines =@@
- index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -38, +27 lines =@@
- index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -65, +54 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.js (38 errors) ====
-+==== index.js (27 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
-@@= skipped -91, +69 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.cjs (38 errors) ====
-+==== index.cjs (27 errors) ====
-     // ESM-format imports below should issue errors
-     import * as m1 from "./index.js";
-                         ~~~~~~~~~~~~
-@@= skipped -74, +74 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
-@@= skipped -91, +69 lines =@@
-     // cjs format file
-     const x = 1;
-     export {x};
--==== index.mjs (38 errors) ====
-+==== index.mjs (27 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node18).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node18).errors.txt.diff
deleted file mode 100644
index aff003ddc2..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=node18).errors.txt.diff
+++ /dev/null
@@ -1,236 +0,0 @@
---- old.nodeModulesAllowJs1(module=node18).errors.txt
-+++ new.nodeModulesAllowJs1(module=node18).errors.txt
-@@= skipped -8, +8 lines =@@
- index.cjs(23,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another")' call instead.
- index.cjs(24,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/")' call instead.
- index.cjs(25,22): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("./subfolder2/another/index")' call instead.
--index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(51,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(52,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(59,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(60,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(61,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -38, +27 lines =@@
- index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -38, +27 lines =@@
- index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(50,22): error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(51,22): error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(58,22): error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(59,22): error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(60,22): error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
- index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
-@@= skipped -65, +54 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.js (38 errors) ====
-+==== index.js (27 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
-@@= skipped -91, +69 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.cjs (38 errors) ====
-+==== index.cjs (27 errors) ====
-     // ESM-format imports below should issue errors
-     import * as m1 from "./index.js";
-                         ~~~~~~~~~~~~
-@@= skipped -74, +74 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
-@@= skipped -91, +69 lines =@@
-     // cjs format file
-     const x = 1;
-     export {x};
--==== index.mjs (38 errors) ====
-+==== index.mjs (27 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~
- !!! error TS1471: Module './' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~
- !!! error TS1471: Module './index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- !!! error TS1471: Module './subfolder2/another/index' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     void m24;
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt.diff
deleted file mode 100644
index f3b05ae21c..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJs1(module=nodenext).errors.txt.diff
+++ /dev/null
@@ -1,197 +0,0 @@
---- old.nodeModulesAllowJs1(module=nodenext).errors.txt
-+++ new.nodeModulesAllowJs1(module=nodenext).errors.txt
-@@= skipped -0, +0 lines =@@
--index.cjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.cjs(61,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.cjs(75,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.cjs(76,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
- index.cjs(77,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
-@@= skipped -30, +19 lines =@@
- index.js(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.js(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.js(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.js(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
- index.js(76,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
-@@= skipped -33, +22 lines =@@
- index.mjs(22,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(23,22): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
- index.mjs(24,22): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './subfolder2/another/index.mjs'?
--index.mjs(50,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(51,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(52,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(53,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(54,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(55,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(56,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(57,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(58,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(59,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.mjs(60,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.mjs(74,21): error TS2307: Cannot find module './' or its corresponding type declarations.
- index.mjs(75,21): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './index.mjs'?
- index.mjs(76,21): error TS2834: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Consider adding an extension to the import path.
-@@= skipped -60, +49 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.js (33 errors) ====
-+==== index.js (22 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     void m24;
-     void m25;
-     void m26;
-@@= skipped -81, +59 lines =@@
-     // esm format file
-     const x = 1;
-     export {x};
--==== index.cjs (22 errors) ====
-+==== index.cjs (11 errors) ====
-     // ESM-format imports below should issue errors
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-@@= skipped -52, +52 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     void m24;
-     void m25;
-     void m26;
-@@= skipped -81, +59 lines =@@
-     // cjs format file
-     const x = 1;
-     export {x};
--==== index.mjs (33 errors) ====
-+==== index.mjs (22 errors) ====
-     import * as m1 from "./index.js";
-     import * as m2 from "./index.mjs";
-     import * as m3 from "./index.cjs";
-@@= skipped -73, +73 lines =@@
-     
-     // These should _mostly_ work - `import = require` always desugars to require calls, which do have extension and index resolution (but can't load anything that resolves to esm!)
-     import m24 = require("./");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m25 = require("./index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m26 = require("./subfolder");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m27 = require("./subfolder/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m28 = require("./subfolder/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m29 = require("./subfolder2");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m30 = require("./subfolder2/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m31 = require("./subfolder2/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m32 = require("./subfolder2/another");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m33 = require("./subfolder2/another/");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     import m34 = require("./subfolder2/another/index");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     void m24;
-     void m25;
-     void m26;
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt.diff
index f1ab5818bb..623a2be03a 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node16).errors.txt.diff
@@ -4,34 +4,9 @@
 -file.js(4,1): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
 +file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
  index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (1 errors) ====
-+
-+
-+==== subfolder/index.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     export = a;
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== subfolder/file.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     module.exports = a;
--==== index.js (2 errors) ====
-+==== index.js (1 errors) ====
-     // esm format file
-     const a = {};
-     export = a;
-     ~~~~~~~~~~~
- !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== file.js (1 errors) ====
-     // esm format file
+ index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+ subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+@@= skipped -26, +26 lines =@@
      import "fs";
      const a = {};
      module.exports = a;
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt.diff
index b1a763b122..31a49d11f9 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=node18).errors.txt.diff
@@ -4,34 +4,9 @@
 -file.js(4,1): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
 +file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
  index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (1 errors) ====
-+
-+
-+==== subfolder/index.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     export = a;
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== subfolder/file.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     module.exports = a;
--==== index.js (2 errors) ====
-+==== index.js (1 errors) ====
-     // esm format file
-     const a = {};
-     export = a;
-     ~~~~~~~~~~~
- !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== file.js (1 errors) ====
-     // esm format file
+ index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+ subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+@@= skipped -26, +26 lines =@@
      import "fs";
      const a = {};
      module.exports = a;
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt.diff
index 29f6faa7d2..ed88e6d3b2 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsExportAssignment(module=nodenext).errors.txt.diff
@@ -4,34 +4,9 @@
 -file.js(4,1): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
 +file.js(4,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
  index.js(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (1 errors) ====
-+
-+
-+==== subfolder/index.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     export = a;
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== subfolder/file.js (0 errors) ====
-     // cjs format file
-     const a = {};
-     module.exports = a;
--==== index.js (2 errors) ====
-+==== index.js (1 errors) ====
-     // esm format file
-     const a = {};
-     export = a;
-     ~~~~~~~~~~~
- !!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
--    ~~~~~~~~~~~
--!!! error TS8003: 'export =' can only be used in TypeScript files.
- ==== file.js (1 errors) ====
-     // esm format file
+ index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+ subfolder/index.js(3,1): error TS8003: 'export =' can only be used in TypeScript files.
+@@= skipped -26, +26 lines =@@
      import "fs";
      const a = {};
      module.exports = a;
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt.diff
deleted file mode 100644
index fe0f2883f0..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node16).errors.txt.diff
+++ /dev/null
@@ -1,53 +0,0 @@
---- old.nodeModulesAllowJsImportAssignment(module=node16).errors.txt
-+++ new.nodeModulesAllowJsImportAssignment(module=node16).errors.txt
-@@= skipped -0, +0 lines =@@
--file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (2 errors) ====
--    // cjs format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== index.js (2 errors) ====
--    // esm format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== file.js (2 errors) ====
--    // esm format file
--    const __require = null;
--    const _createRequire = null;
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== package.json (0 errors) ====
--    {
--        "name": "package",
--        "private": true,
--        "type": "module"
--    }
--==== subfolder/package.json (0 errors) ====
--    {
--        "type": "commonjs"
--    }
--==== types.d.ts (0 errors) ====
--    declare module "fs";
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt.diff
deleted file mode 100644
index aa38396f6b..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=node18).errors.txt.diff
+++ /dev/null
@@ -1,53 +0,0 @@
---- old.nodeModulesAllowJsImportAssignment(module=node18).errors.txt
-+++ new.nodeModulesAllowJsImportAssignment(module=node18).errors.txt
-@@= skipped -0, +0 lines =@@
--file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (2 errors) ====
--    // cjs format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== index.js (2 errors) ====
--    // esm format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== file.js (2 errors) ====
--    // esm format file
--    const __require = null;
--    const _createRequire = null;
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== package.json (0 errors) ====
--    {
--        "name": "package",
--        "private": true,
--        "type": "module"
--    }
--==== subfolder/package.json (0 errors) ====
--    {
--        "type": "commonjs"
--    }
--==== types.d.ts (0 errors) ====
--    declare module "fs";
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt.diff
deleted file mode 100644
index 6e1f15e324..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt.diff
+++ /dev/null
@@ -1,53 +0,0 @@
---- old.nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt
-+++ new.nodeModulesAllowJsImportAssignment(module=nodenext).errors.txt
-@@= skipped -0, +0 lines =@@
--file.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--file.js(6,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(2,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(4,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (2 errors) ====
--    // cjs format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== index.js (2 errors) ====
--    // esm format file
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== file.js (2 errors) ====
--    // esm format file
--    const __require = null;
--    const _createRequire = null;
--    import fs = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    fs.readFile;
--    export import fs2 = require("fs");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--==== package.json (0 errors) ====
--    {
--        "name": "package",
--        "private": true,
--        "type": "module"
--    }
--==== subfolder/package.json (0 errors) ====
--    {
--        "type": "commonjs"
--    }
--==== types.d.ts (0 errors) ====
--    declare module "fs";
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt.diff
deleted file mode 100644
index 31b8fd889e..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt.diff
+++ /dev/null
@@ -1,52 +0,0 @@
---- old.nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt
-+++ new.nodeModulesAllowJsSynchronousCallErrors(module=node16).errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(3,22): error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- subfolder/index.js(2,17): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
-   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
--subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- subfolder/index.js(3,22): error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (4 errors) ====
-+
-+
-+==== subfolder/index.js (2 errors) ====
-     // cjs format file
-     import {h} from "../index.js";
-                     ~~~~~~~~~~~~~
- !!! error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
- !!! error TS1479:   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
-     import mod = require("../index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~
- !!! error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import {f as _f} from "./index.js";
-     import mod2 = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     export async function f() {
-         const mod3 = await import ("../index.js");
-         const mod4 = await import ("./index.js");
-         h();
-     }
--==== index.js (3 errors) ====
-+==== index.js (1 errors) ====
-     // esm format file
-     import {h as _h} from "./index.js";
-     import mod = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~
- !!! error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import {f} from "./subfolder/index.js";
-     import mod2 = require("./subfolder/index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     export async function h() {
-         const mod3 = await import ("./index.js");
-         const mod4 = await import ("./subfolder/index.js");
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt.diff
deleted file mode 100644
index 8ab98c1b2e..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt.diff
+++ /dev/null
@@ -1,52 +0,0 @@
---- old.nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt
-+++ new.nodeModulesAllowJsSynchronousCallErrors(module=node18).errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- index.js(3,22): error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- subfolder/index.js(2,17): error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
-   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
--subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
- subfolder/index.js(3,22): error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
--subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (4 errors) ====
-+
-+
-+==== subfolder/index.js (2 errors) ====
-     // cjs format file
-     import {h} from "../index.js";
-                     ~~~~~~~~~~~~~
- !!! error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("../index.js")' call instead.
- !!! error TS1479:   To convert this file to an ECMAScript module, change its file extension to '.mjs' or create a local package.json file with `{ "type": "module" }`.
-     import mod = require("../index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~~
- !!! error TS1471: Module '../index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import {f as _f} from "./index.js";
-     import mod2 = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     export async function f() {
-         const mod3 = await import ("../index.js");
-         const mod4 = await import ("./index.js");
-         h();
-     }
--==== index.js (3 errors) ====
-+==== index.js (1 errors) ====
-     // esm format file
-     import {h as _h} from "./index.js";
-     import mod = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-                          ~~~~~~~~~~~~
- !!! error TS1471: Module './index.js' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported with 'require'. Use an ECMAScript import instead.
-     import {f} from "./subfolder/index.js";
-     import mod2 = require("./subfolder/index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
-     export async function h() {
-         const mod3 = await import ("./index.js");
-         const mod4 = await import ("./subfolder/index.js");
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt.diff
deleted file mode 100644
index 4c5b8ad1b8..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt.diff
+++ /dev/null
@@ -1,50 +0,0 @@
---- old.nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt
-+++ new.nodeModulesAllowJsSynchronousCallErrors(module=nodenext).errors.txt
-@@= skipped -0, +0 lines =@@
--index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(3,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--subfolder/index.js(5,1): error TS8002: 'import ... =' can only be used in TypeScript files.
--
--
--==== subfolder/index.js (2 errors) ====
--    // cjs format file
--    import {h} from "../index.js";
--    import mod = require("../index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    import {f as _f} from "./index.js";
--    import mod2 = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    export async function f() {
--        const mod3 = await import ("../index.js");
--        const mod4 = await import ("./index.js");
--        h();
--    }
--==== index.js (2 errors) ====
--    // esm format file
--    import {h as _h} from "./index.js";
--    import mod = require("./index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    import {f} from "./subfolder/index.js";
--    import mod2 = require("./subfolder/index.js");
--    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--!!! error TS8002: 'import ... =' can only be used in TypeScript files.
--    export async function h() {
--        const mod3 = await import ("./index.js");
--        const mod4 = await import ("./subfolder/index.js");
--        f();
--    }
--==== package.json (0 errors) ====
--    {
--        "name": "package",
--        "private": true,
--        "type": "module"
--    }
--==== subfolder/package.json (0 errors) ====
--    {
--        "type": "commonjs"
--    }
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/override_js3.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/override_js3.errors.txt.diff
deleted file mode 100644
index 81561936e0..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/override_js3.errors.txt.diff
+++ /dev/null
@@ -1,21 +0,0 @@
---- old.override_js3.errors.txt
-+++ new.override_js3.errors.txt
-@@= skipped -0, +0 lines =@@
--a.js(7,5): error TS8009: The 'override' modifier can only be used in TypeScript files.
--
--
--==== a.js (1 errors) ====
--    class B {
--        foo (v) {}
--        fooo (v) {}
--    }
--    
--    class D extends B {
--        override foo (v) {}
--        ~~~~~~~~
--!!! error TS8009: The 'override' modifier can only be used in TypeScript files.
--        /** @override */
--        fooo (v) {}
--    }
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression10.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression10.errors.txt.diff
deleted file mode 100644
index d76c5a0954..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression10.errors.txt.diff
+++ /dev/null
@@ -1,25 +0,0 @@
---- old.parserArrowFunctionExpression10.errors.txt
-+++ new.parserArrowFunctionExpression10.errors.txt
-@@= skipped -0, +0 lines =@@
- fileJs.js(1,1): error TS2304: Cannot find name 'a'.
- fileJs.js(1,11): error TS2304: Cannot find name 'c'.
--fileJs.js(1,11): error TS8010: Type annotations can only be used in TypeScript files.
- fileJs.js(1,17): error TS2304: Cannot find name 'd'.
- fileJs.js(1,27): error TS2304: Cannot find name 'f'.
- fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
-@@= skipped -8, +7 lines =@@
- fileTs.ts(1,27): error TS2304: Cannot find name 'f'.
-
-
--==== fileJs.js (5 errors) ====
-+==== fileJs.js (4 errors) ====
-     a ? (b) : c => (d) : e => f // Not legal JS; "Unexpected token ':'" at last colon
-     ~
- !!! error TS2304: Cannot find name 'a'.
-               ~
- !!! error TS2304: Cannot find name 'c'.
--              ~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-                     ~
- !!! error TS2304: Cannot find name 'd'.
-                               ~
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression13.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression13.errors.txt.diff
deleted file mode 100644
index b4e708c936..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression13.errors.txt.diff
+++ /dev/null
@@ -1,22 +0,0 @@
---- old.parserArrowFunctionExpression13.errors.txt
-+++ new.parserArrowFunctionExpression13.errors.txt
-@@= skipped -0, +0 lines =@@
- fileJs.js(1,1): error TS2304: Cannot find name 'a'.
- fileJs.js(1,11): error TS2304: Cannot find name 'a'.
--fileJs.js(1,21): error TS8010: Type annotations can only be used in TypeScript files.
- fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
- fileTs.ts(1,11): error TS2304: Cannot find name 'a'.
-
-
--==== fileJs.js (3 errors) ====
-+==== fileJs.js (2 errors) ====
-     a ? () => a() : (): any => null; // Not legal JS; "Unexpected token ')'" at last paren
-     ~
- !!! error TS2304: Cannot find name 'a'.
-               ~
- !!! error TS2304: Cannot find name 'a'.
--                        ~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-     
- ==== fileTs.ts (2 errors) ====
-     a ? () => a() : (): any => null;
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression14.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression14.errors.txt.diff
deleted file mode 100644
index c4705940d8..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression14.errors.txt.diff
+++ /dev/null
@@ -1,31 +0,0 @@
---- old.parserArrowFunctionExpression14.errors.txt
-+++ new.parserArrowFunctionExpression14.errors.txt
-@@= skipped -0, +0 lines =@@
- fileJs.js(1,1): error TS2304: Cannot find name 'a'.
--fileJs.js(1,11): error TS8010: Type annotations can only be used in TypeScript files.
--fileJs.js(1,20): error TS8009: The '?' modifier can only be used in TypeScript files.
--fileJs.js(1,23): error TS8010: Type annotations can only be used in TypeScript files.
--fileJs.js(1,32): error TS8010: Type annotations can only be used in TypeScript files.
- fileJs.js(1,40): error TS2304: Cannot find name 'd'.
- fileJs.js(1,46): error TS2304: Cannot find name 'e'.
- fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
-@@= skipped -9, +5 lines =@@
- fileTs.ts(1,46): error TS2304: Cannot find name 'e'.
-
-
--==== fileJs.js (7 errors) ====
-+==== fileJs.js (3 errors) ====
-     a() ? (b: number, c?: string): void => d() : e; // Not legal JS; "Unexpected token ':'" at first colon
-     ~
- !!! error TS2304: Cannot find name 'a'.
--              ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--                       ~
--!!! error TS8009: The '?' modifier can only be used in TypeScript files.
--                          ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--                                   ~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-                                            ~
- !!! error TS2304: Cannot find name 'd'.
-                                                  ~
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression15.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression15.errors.txt.diff
deleted file mode 100644
index 7b1e6d7782..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression15.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.parserArrowFunctionExpression15.errors.txt
-+++ new.parserArrowFunctionExpression15.errors.txt
-@@= skipped -0, +0 lines =@@
--fileJs.js(1,18): error TS8010: Type annotations can only be used in TypeScript files.
--
--
--==== fileJs.js (1 errors) ====
--    false ? (param): string => param : null // Not legal JS; "Unexpected token ':'" at last colon
--                     ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    
--==== fileTs.ts (0 errors) ====
--    false ? (param): string => param : null
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression16.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression16.errors.txt.diff
deleted file mode 100644
index da8b37a944..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression16.errors.txt.diff
+++ /dev/null
@@ -1,15 +0,0 @@
---- old.parserArrowFunctionExpression16.errors.txt
-+++ new.parserArrowFunctionExpression16.errors.txt
-@@= skipped -0, +0 lines =@@
--fileJs.js(1,25): error TS8010: Type annotations can only be used in TypeScript files.
--
--
--==== fileJs.js (1 errors) ====
--    true ? false ? (param): string => param : null : null // Not legal JS; "Unexpected token ':'" at last colon
--                            ~~~~~~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
--    
--==== fileTs.ts (0 errors) ====
--    true ? false ? (param): string => param : null : null
--    
-+<no content>
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression17.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression17.errors.txt.diff
deleted file mode 100644
index 5d502ccdfd..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/parserArrowFunctionExpression17.errors.txt.diff
+++ /dev/null
@@ -1,28 +0,0 @@
---- old.parserArrowFunctionExpression17.errors.txt
-+++ new.parserArrowFunctionExpression17.errors.txt
-@@= skipped -0, +0 lines =@@
- fileJs.js(1,1): error TS2304: Cannot find name 'a'.
- fileJs.js(1,5): error TS2304: Cannot find name 'b'.
- fileJs.js(1,15): error TS2304: Cannot find name 'd'.
--fileJs.js(1,15): error TS8010: Type annotations can only be used in TypeScript files.
- fileJs.js(1,20): error TS2304: Cannot find name 'e'.
- fileTs.ts(1,1): error TS2304: Cannot find name 'a'.
- fileTs.ts(1,5): error TS2304: Cannot find name 'b'.
-@@= skipped -8, +7 lines =@@
- fileTs.ts(1,20): error TS2304: Cannot find name 'e'.
-
-
--==== fileJs.js (5 errors) ====
-+==== fileJs.js (4 errors) ====
-     a ? b : (c) : d => e // Not legal JS; "Unexpected token ':'" at last colon
-     ~
- !!! error TS2304: Cannot find name 'a'.
-@@= skipped -8, +8 lines =@@
- !!! error TS2304: Cannot find name 'b'.
-                   ~
- !!! error TS2304: Cannot find name 'd'.
--                  ~
--!!! error TS8010: Type annotations can only be used in TypeScript files.
-                        ~
- !!! error TS2304: Cannot find name 'e'.
-     
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/plainJSGrammarErrors.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/plainJSGrammarErrors.errors.txt.diff
deleted file mode 100644
index 56d5793373..0000000000
--- a/testdata/baselines/reference/submoduleAccepted/conformance/plainJSGrammarErrors.errors.txt.diff
+++ /dev/null
@@ -1,114 +0,0 @@
---- old.plainJSGrammarErrors.errors.txt
-+++ new.plainJSGrammarErrors.errors.txt
-@@= skipped -4, +4 lines =@@
- plainJSGrammarErrors.js(17,9): error TS18041: A 'return' statement cannot be used inside a class static block.
- plainJSGrammarErrors.js(20,5): error TS1089: 'static' modifier cannot appear on a constructor declaration.
- plainJSGrammarErrors.js(21,5): error TS1089: 'async' modifier cannot appear on a constructor declaration.
--plainJSGrammarErrors.js(22,5): error TS8009: The 'const' modifier can only be used in TypeScript files.
- plainJSGrammarErrors.js(22,11): error TS1248: A class member cannot have the 'const' keyword.
--plainJSGrammarErrors.js(23,5): error TS8009: The 'const' modifier can only be used in TypeScript files.
- plainJSGrammarErrors.js(23,11): error TS1248: A class member cannot have the 'const' keyword.
- plainJSGrammarErrors.js(26,11): error TS1030: 'async' modifier already seen.
- plainJSGrammarErrors.js(28,11): error TS1029: 'static' modifier must precede 'async' modifier.
- plainJSGrammarErrors.js(29,5): error TS1031: 'export' modifier cannot appear on class elements of this kind.
--plainJSGrammarErrors.js(29,5): error TS8009: The 'export' modifier can only be used in TypeScript files.
- plainJSGrammarErrors.js(30,5): error TS1031: 'export' modifier cannot appear on class elements of this kind.
- plainJSGrammarErrors.js(34,22): error TS1005: '{' expected.
- plainJSGrammarErrors.js(35,9): error TS1054: A 'get' accessor cannot have parameters.
-@@= skipped -24, +21 lines =@@
- plainJSGrammarErrors.js(54,8): error TS1030: 'export' modifier already seen.
- plainJSGrammarErrors.js(55,8): error TS1044: 'static' modifier cannot appear on a module or namespace element.
- plainJSGrammarErrors.js(56,22): error TS1090: 'static' modifier cannot appear on a parameter.
--plainJSGrammarErrors.js(56,22): error TS8012: Parameter modifiers can only be used in TypeScript files.
- plainJSGrammarErrors.js(57,7): error TS1029: 'export' modifier must precede 'async' modifier.
- plainJSGrammarErrors.js(58,26): error TS1090: 'export' modifier cannot appear on a parameter.
--plainJSGrammarErrors.js(58,26): error TS8012: Parameter modifiers can only be used in TypeScript files.
- plainJSGrammarErrors.js(59,25): error TS1090: 'async' modifier cannot appear on a parameter.
--plainJSGrammarErrors.js(59,25): error TS8012: Parameter modifiers can only be used in TypeScript files.
- plainJSGrammarErrors.js(60,7): error TS1030: 'async' modifier already seen.
- plainJSGrammarErrors.js(61,1): error TS1042: 'async' modifier cannot be used here.
- plainJSGrammarErrors.js(62,5): error TS1042: 'async' modifier cannot be used here.
--plainJSGrammarErrors.js(62,5): error TS8009: The 'async' modifier can only be used in TypeScript files.
- plainJSGrammarErrors.js(64,1): error TS1042: 'async' modifier cannot be used here.
- plainJSGrammarErrors.js(65,1): error TS1042: 'async' modifier cannot be used here.
- plainJSGrammarErrors.js(66,1): error TS1042: 'async' modifier cannot be used here.
-@@= skipped -38, +34 lines =@@
- plainJSGrammarErrors.js(106,5): error TS1042: 'export' modifier cannot be used here.
- plainJSGrammarErrors.js(108,25): error TS1162: An object member cannot be declared optional.
- plainJSGrammarErrors.js(109,6): error TS1162: An object member cannot be declared optional.
--plainJSGrammarErrors.js(109,6): error TS8009: The '?' modifier can only be used in TypeScript files.
- plainJSGrammarErrors.js(110,15): error TS1255: A definite assignment assertion '!' is not permitted in this context.
- plainJSGrammarErrors.js(111,19): error TS1255: A definite assignment assertion '!' is not permitted in this context.
- plainJSGrammarErrors.js(114,16): error TS1312: Did you mean to use a ':'? An '=' can only follow a property name when the containing object literal is part of a destructuring pattern.
-@@= skipped -35, +34 lines =@@
- plainJSGrammarErrors.js(205,36): error TS1325: Argument of dynamic import cannot be spread element.
-
-
--==== plainJSGrammarErrors.js (102 errors) ====
-+==== plainJSGrammarErrors.js (94 errors) ====
-     class C {
-         // #private mistakes
-         q = #unbound
-@@= skipped -37, +37 lines =@@
-         ~~~~~
- !!! error TS1089: 'async' modifier cannot appear on a constructor declaration.
-         const x = 1
--        ~~~~~
--!!! error TS8009: The 'const' modifier can only be used in TypeScript files.
-               ~
- !!! error TS1248: A class member cannot have the 'const' keyword.
-         const y() {
--        ~~~~~
--!!! error TS8009: The 'const' modifier can only be used in TypeScript files.
-               ~
- !!! error TS1248: A class member cannot have the 'const' keyword.
-             return 12
-@@= skipped -21, +17 lines =@@
-         export cantExportProperty = 1
-         ~~~~~~
- !!! error TS1031: 'export' modifier cannot appear on class elements of this kind.
--        ~~~~~~
--!!! error TS8009: The 'export' modifier can only be used in TypeScript files.
-         export cantExportMethod() {
-         ~~~~~~
- !!! error TS1031: 'export' modifier cannot appear on class elements of this kind.
-@@= skipped -61, +59 lines =@@
-     function staticParam(static x = 1) { return x }
-                          ~~~~~~
- !!! error TS1090: 'static' modifier cannot appear on a parameter.
--                         ~~~~~~
--!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
-     async export function oorder(x = 1) { return x }
-           ~~~~~~
- !!! error TS1029: 'export' modifier must precede 'async' modifier.
-     function cantExportParam(export x = 1) { return x }
-                              ~~~~~~
- !!! error TS1090: 'export' modifier cannot appear on a parameter.
--                             ~~~~~~
--!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
-     function cantAsyncParam(async x = 1) { return x }
-                             ~~~~~
- !!! error TS1090: 'async' modifier cannot appear on a parameter.
--                            ~~~~~
--!!! error TS8012: Parameter modifiers can only be used in TypeScript files.
-     async async function extremelyAsync() {}
-           ~~~~~
- !!! error TS1030: 'async' modifier already seen.
-@@= skipped -24, +18 lines =@@
-         async cantAsyncPropert = 1
-         ~~~~~
- !!! error TS1042: 'async' modifier cannot be used here.
--        ~~~~~
--!!! error TS8009: The 'async' modifier can only be used in TypeScript files.
-     }
-     async const cantAsyncConst = 2
-     ~~~~~
-@@= skipped -105, +103 lines =@@
-         m?() { return 12 },
-          ~
- !!! error TS1162: An object member cannot be declared optional.
--         ~
--!!! error TS8009: The '?' modifier can only be used in TypeScript files.
-         definitely!,
-                   ~
- !!! error TS1255: A definite assignment assertion '!' is not permitted in this context.
\ No newline at end of file
diff --git a/testdata/baselines/reference/submoduleAccepted/conformance/typeSatisfaction_js.errors.txt.diff b/testdata/baselines/reference/submoduleAccepted/conformance/typeSatisfaction_js.errors.txt.diff
index 05a8be7c26..8dce7333c0 100644
--- a/testdata/baselines/reference/submoduleAccepted/conformance/typeSatisfaction_js.errors.txt.diff
+++ b/testdata/baselines/reference/submoduleAccepted/conformance/typeSatisfaction_js.errors.txt.diff
@@ -1,20 +1,15 @@
 --- old.typeSatisfaction_js.errors.txt
 +++ new.typeSatisfaction_js.errors.txt
 @@= skipped -0, +0 lines =@@
--/src/a.js(1,29): error TS8037: Type satisfaction expressions can only be used in TypeScript files.
--
--
--==== /src/a.js (1 errors) ====
 +error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-+
-+
+ /src/a.js(1,29): error TS8037: Type satisfaction expressions can only be used in TypeScript files.
+
+
 +!!! error TS5055: Cannot write file '/src/a.js' because it would overwrite input file.
 +!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
 +!!! error TS5102: Option 'outFile' has been removed. Please remove it from your configuration.
-+==== /src/a.js (0 errors) ====
+ ==== /src/a.js (1 errors) ====
      var v = undefined satisfies 1;
--                                ~
--!!! error TS8037: Type satisfaction expressions can only be used in TypeScript files.
-     
\ No newline at end of file
+                                 ~
\ No newline at end of file
diff --git a/testdata/tests/cases/compiler/jsSyntacticDiagnostics.ts b/testdata/tests/cases/compiler/jsSyntacticDiagnostics.ts
new file mode 100644
index 0000000000..0c087ddc15
--- /dev/null
+++ b/testdata/tests/cases/compiler/jsSyntacticDiagnostics.ts
@@ -0,0 +1,102 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+
+// @filename: test.js
+
+// Type annotations should be flagged as errors
+function func(x: number): string {
+    return x.toString();
+}
+
+// Interface declarations should be flagged as errors
+interface Person {
+    name: string;
+    age: number;
+}
+
+// Type alias declarations should be flagged as errors
+type StringOrNumber = string | number;
+
+// Enum declarations should be flagged as errors
+enum Color {
+    Red,
+    Green,
+    Blue
+}
+
+// Module declarations should be flagged as errors
+module MyModule {
+    export var x = 1;
+}
+
+// Namespace declarations should be flagged as errors
+namespace MyNamespace {
+    export var y = 2;
+}
+
+// Non-null assertions should be flagged as errors
+let value = getValue()!;
+
+// Type assertions should be flagged as errors
+let result = (value as string).toUpperCase();
+
+// Satisfies expressions should be flagged as errors
+let config = {} satisfies Config;
+
+// Import type should be flagged as errors
+import type { SomeType } from './other';
+
+// Export type should be flagged as errors
+export type { SomeType };
+
+// Import equals should be flagged as errors
+import lib = require('./lib');
+
+// Export equals should be flagged as errors
+export = MyModule;
+
+// TypeScript modifiers should be flagged as errors
+class MyClass {
+    public name: string;
+    private age: number;
+    protected id: number;
+    readonly value: number;
+    
+    constructor(public x: number, private y: number) {
+        this.name = '';
+        this.age = 0;
+        this.id = 0;
+        this.value = 0;
+    }
+}
+
+// Optional parameters should be flagged as errors
+function optionalParam(x?: number) {
+    return x || 0;
+}
+
+// Signature declarations should be flagged as errors
+function signatureOnly(x: number): string;
+
+// Type parameters should be flagged as errors
+function generic<T>(x: T): T {
+    return x;
+}
+
+// Type arguments should be flagged as errors
+let array = Array<string>();
+
+// Implements clause should be flagged as errors
+class MyClassWithImplements implements Person {
+    name = '';
+    age = 0;
+}
+
+function getValue(): any {
+    return null;
+}
+
+interface Config {
+    name: string;
+}
\ No newline at end of file