Typesafe array fill

package.json

@@ -72,6 +72,11 @@
       "types": "./dist/array-index-of.d.ts",
       "import": "./dist/array-index-of.mjs",
       "default": "./dist/array-index-of.js"
+    },
+    "./array-fill": {
+      "types": "./dist/array-fill.d.ts",
+      "import": "./dist/array-fill.mjs",
+      "default": "./dist/array-fill.js"
     }
   },
   "keywords": [],

src/entrypoints/array-fill.d.ts

@@ -0,0 +1,28 @@
+/// <reference path="utils.d.ts" />
+
+// TODO: See how to remove the fill method from the interface completely
+interface ReadonlyArray<T> {
+  fill: never;
+}
+
+// TODO: See how to override the fill method so that an Array<T>.fill<U> makes the Array<T> an Array<U>
+
+interface Array<T> {
+  fill<U>(
+    value: U | (TSReset.WidenLiteral<U> & {}),
+    start?: undefined,
+    end?: undefined,
+  ): (U | (TSReset.WidenLiteral<U> & {}))[];
+
+  fill<U>(
+    value: U | (TSReset.WidenLiteral<U> & {}),
+    start: 0,
+    end?: undefined,
+  ): (U | (TSReset.WidenLiteral<U> & {}))[];
+
+  fill<U>(
+    value: U | (TSReset.WidenLiteral<U> & {}),
+    start: number,
+    end?: number,
+  ): (T | (U | (TSReset.WidenLiteral<U> & {})))[];
+}

src/entrypoints/recommended.d.ts

@@ -6,3 +6,4 @@
 /// <reference path="set-has.d.ts" />
 /// <reference path="map-has.d.ts" />
 /// <reference path="array-index-of.d.ts" />
+/// <reference path="array-fill.d.ts" />

src/tests/array-fill.ts

@@ -0,0 +1,67 @@
+import { doNotExecute, Equal, Expect } from "./utils";
+
+// TODO: Add tests that check the type overrides for the fill method once they are implemented
+
+doNotExecute(() => {
+  const arr = [] as const;
+
+  // @ts-expect-error
+  arr.fill(2);
+});
+
+doNotExecute(() => {
+  const arr = [1, "2", { a: 3 }, []];
+
+  const newArr = arr.fill(2);
+
+  // @ts-expect-error
+  type Test = Expect<Equal<typeof newArr, typeof arr>>;
+});
+
+doNotExecute(() => {
+  const arr = [1, "2", { a: 3 }, []];
+
+  const newArr = arr.fill(2);
+
+  type Test = Expect<Equal<typeof newArr, number[]>>;
+});
+
+doNotExecute(() => {
+  const arr = [1, "2", { a: 3 }, []];
+
+  const newArr = arr.fill({ b: 1 } as const);
+
+  type Test = Expect<
+    Equal<
+      typeof newArr,
+      {
+        readonly b: 1;
+      }[]
+    >
+  >;
+});
+
+doNotExecute(() => {
+  const arr = [1, "2", { a: 3 }, []];
+
+  const newArr = arr.fill(2, 0);
+
+  // @ts-expect-error
+  type Test = Expect<Equal<typeof newArr, typeof arr>>;
+});
+
+doNotExecute(() => {
+  const arr = [1, "2", { a: 3 }, []];
+
+  const newArr = arr.fill(2, 0);
+
+  type Test = Expect<Equal<typeof newArr, number[]>>;
+});
+
+doNotExecute(() => {
+  const arr = ["2", { a: 3 }, []];
+
+  const newArr = arr.fill(2, 1);
+
+  type Test = Expect<Equal<typeof newArr, (number | (typeof arr)[number])[]>>;
+});