LibJS: Implement Array.prototype.toReversed()

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

@@ -252,6 +252,7 @@ describe("ability to work with generic non-array objects", () => {
     });
 
     test("reverse", () => {
+        const o = { length: 5, 0: "foo", 1: "bar", 3: "baz" };
         expect(Array.prototype.reverse.call(o)).toEqual({
             length: 5,
             4: "foo",
@@ -341,4 +342,10 @@ describe("ability to work with generic non-array objects", () => {
         const trueResult = result.get(trueObject);
         expect(trueResult).toEqual(["bar", "baz"]);
     });
+
+    test("toReversed", () => {
+        const result = Array.prototype.toReversed.call(o);
+        expect(result).toEqual([undefined, "baz", undefined, "bar", "foo"]);
+        expect(result).not.toBe(o);
+    });
 });

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

@@ -0,0 +1,39 @@
+describe("normal behavior", () => {
+    test("length is 0", () => {
+        expect(Array.prototype.toReversed).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const a = [1, 2, 3, 4, 5];
+        const b = a.toReversed();
+        expect(a).not.toBe(b);
+        expect(a).toEqual([1, 2, 3, 4, 5]);
+        expect(b).toEqual([5, 4, 3, 2, 1]);
+    });
+
+    test("is unscopable", () => {
+        expect(Array.prototype[Symbol.unscopables].toReversed).toBeTrue();
+        const array = [];
+        with (array) {
+            expect(() => {
+                toReversed;
+            }).toThrowWithMessage(ReferenceError, "'toReversed' is not defined");
+        }
+    });
+});
+
+describe("errors", () => {
+    test("null or undefined this value", () => {
+        expect(() => {
+            Array.prototype.toReversed.call();
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+
+        expect(() => {
+            Array.prototype.toReversed.call(undefined);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+
+        expect(() => {
+            Array.prototype.toReversed.call(null);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+    });
+});