feat(react-scripts): check Node.js version early in CLI (#5430)

packages/react-scripts/bin/react-scripts.js

@@ -8,6 +8,20 @@
 
 'use strict';
 
+// Check Node.js version early for clearer errors (see #5430)
+const currentNodeVersion = process.versions.node;
+const [major] = currentNodeVersion.split('.');
+if (Number(major) < 14) {
+  console.error(
+    'You are running Node ' +
+      currentNodeVersion +
+      '.\n' +
+      'react-scripts requires Node 14 or higher. \n' +
+      'Please update your version of Node.'
+  );
+  process.exit(1);
+}
+
 // Makes the script crash on unhandled rejections instead of silently
 // ignoring them. In the future, promise rejections that are not handled will
 // terminate the Node.js process with a non-zero exit code.

packages/react-scripts/scripts/eject.js

@@ -237,8 +237,29 @@ prompts({
 
   // Add Babel config
   console.log(`  Adding ${cyan('Babel')} preset`);
+  // Detect if the new JSX transform is available and prefer it after eject
+  const hasJsxRuntime = (() => {
+    if (process.env.DISABLE_NEW_JSX_TRANSFORM === 'true') {
+      return false;
+    }
+    try {
+      require.resolve('react/jsx-runtime');
+      return true;
+    } catch (e) {
+      return false;
+    }
+  })();
+
   appPackage.babel = {
-    presets: ['react-app'],
+    // Preserve preset with explicit runtime so ejected apps keep working without importing React
+    presets: [
+      [
+        'react-app',
+        {
+          runtime: hasJsxRuntime ? 'automatic' : 'classic',
+        },
+      ],
+    ],
   };
 
   // Add ESlint config