LibJS: Implement Array.prototype.with()

Userland/Libraries/LibJS/Tests/builtins/Array/Array.prototype-generic-functions.js

@@ -360,4 +360,10 @@ describe("ability to work with generic non-array objects", () => {
         expect(result).toEqual(["foo", "hello", "friends", "baz", undefined]);
         expect(result).not.toBe(o);
     });
+
+    test("with", () => {
+        const result = Array.prototype.with.call(o, 2, "hello");
+        expect(result).toEqual(["foo", "bar", "hello", "baz", undefined]);
+        expect(result).not.toBe(o);
+    });
 });

Userland/Libraries/LibJS/Tests/builtins/Array/Array.prototype.with.js

@@ -0,0 +1,46 @@
+describe("normal behavior", () => {
+    test("length is 2", () => {
+        expect(Array.prototype.with).toHaveLength(2);
+    });
+
+    test("basic functionality", () => {
+        const a = [1, 2, 3, 4, 5];
+        const values = [
+            [0, "foo", ["foo", 2, 3, 4, 5]],
+            [-5, "foo", ["foo", 2, 3, 4, 5]],
+            [4, "foo", [1, 2, 3, 4, "foo"]],
+            [-1, "foo", [1, 2, 3, 4, "foo"]],
+        ];
+        for (const [index, value, expected] of values) {
+            const b = a.with(index, value);
+            expect(a).not.toBe(b);
+            expect(a).toEqual([1, 2, 3, 4, 5]);
+            expect(b).toEqual(expected);
+        }
+    });
+});
+
+describe("errors", () => {
+    test("null or undefined this value", () => {
+        expect(() => {
+            Array.prototype.with.call();
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+
+        expect(() => {
+            Array.prototype.with.call(undefined);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+
+        expect(() => {
+            Array.prototype.with.call(null);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+    });
+
+    test("out of range index", () => {
+        expect(() => {
+            [].with(0, "foo");
+        }).toThrowWithMessage(RangeError, "Index 0 is out of range of array length 0");
+        expect(() => {
+            [].with(-1, "foo");
+        }).toThrowWithMessage(RangeError, "Index -1 is out of range of array length 0");
+    });
+});