LibJS: Add %TypedArray%.prototype.toReversed

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -57,6 +57,7 @@ void TypedArrayPrototype::initialize(GlobalObject& object)
     define_native_function(vm.names.filter, filter, 1, attr);
     define_native_function(vm.names.map, map, 1, attr);
     define_native_function(vm.names.toLocaleString, to_locale_string, 0, attr);
+    define_native_function(vm.names.toReversed, to_reversed, 0, attr);
     define_native_function(vm.names.toSorted, to_sorted, 1, attr);
 
     define_native_accessor(*vm.well_known_symbol_to_string_tag(), to_string_tag_getter, nullptr, Attribute::Configurable);
@@ -1512,7 +1513,44 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::to_locale_string)
     return js_string(vm, builder.to_string());
 }
 
-// 1.2.2.1.4 %TypedArray%.prototype.toSorted ( comparefn ) https://tc39.es/proposal-change-array-by-copy/#sec-%typedarray%.prototype.toSorted
+// 1.2.2.1.3 %TypedArray%.prototype.toReversed ( ), https://tc39.es/proposal-change-array-by-copy/#sec-%typedarray%.prototype.toReversed
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::to_reversed)
+{
+    // 1. Let O be the this value.
+    // 2. Perform ? ValidateTypedArray(O).
+    auto* typed_array = TRY(validate_typed_array_from_this(global_object));
+
+    // 3. Let length be O.[[ArrayLength]].
+    auto length = typed_array->array_length();
+
+    // 4. Let A be ? TypedArrayCreateSameType(O, « 𝔽(length) »).
+    MarkedVector<Value> arguments(vm.heap());
+    arguments.empend(length);
+    auto* return_array = TRY(typed_array_create_same_type(global_object, *typed_array, move(arguments)));
+
+    // 5. Let k be 0.
+    // 6. Repeat, while k < length
+    for (size_t k = 0; k < length; k++) {
+        // a. Let from be ! ToString(𝔽(length - k - 1)).
+        auto from = PropertyKey { length - k - 1 };
+
+        // b. Let Pk be ! ToString(𝔽(k)).
+        auto property_key = PropertyKey { k };
+
+        // c. Let fromValue be ! Get(O, from).
+        auto from_value = MUST(typed_array->get(from));
+
+        // d. Perform ! Set(A, Pk, fromValue, true).
+        MUST(return_array->set(property_key, from_value, Object::ShouldThrowExceptions::Yes));
+
+        // e. Set k to k + 1.
+    }
+
+    // 7. Return A.
+    return return_array;
+}
+
+// 1.2.2.1.4 %TypedArray%.prototype.toSorted ( comparefn ), https://tc39.es/proposal-change-array-by-copy/#sec-%typedarray%.prototype.toSorted
 JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::to_sorted)
 {
     auto comparefn = vm.argument(0);

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.h

@@ -52,6 +52,7 @@ class TypedArrayPrototype final : public Object {
     JS_DECLARE_NATIVE_FUNCTION(filter);
     JS_DECLARE_NATIVE_FUNCTION(map);
     JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
+    JS_DECLARE_NATIVE_FUNCTION(to_reversed);
     JS_DECLARE_NATIVE_FUNCTION(to_sorted);
 };
 

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

@@ -0,0 +1,68 @@
+const TYPED_ARRAYS = [
+    Uint8Array,
+    Uint8ClampedArray,
+    Uint16Array,
+    Uint32Array,
+    Int8Array,
+    Int16Array,
+    Int32Array,
+    Float32Array,
+    Float64Array,
+];
+
+const BIGINT_TYPED_ARRAYS = [BigUint64Array, BigInt64Array];
+
+test("length is 0", () => {
+    TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.toReversed).toHaveLength(0);
+    });
+
+    BIGINT_TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.toReversed).toHaveLength(0);
+    });
+});
+
+describe("basic functionality", () => {
+    test("Odd length array", () => {
+        TYPED_ARRAYS.forEach(T => {
+            const array = new T([1, 2, 3]);
+
+            expect(array.toReversed()).toEqual([3, 2, 1]);
+            expect(array).toEqual([1, 2, 3]);
+        });
+
+        BIGINT_TYPED_ARRAYS.forEach(T => {
+            const array = new T([1n, 2n, 3n]);
+            expect(array.toReversed()).toEqual([3n, 2n, 1n]);
+            expect(array).toEqual([1n, 2n, 3n]);
+        });
+    });
+
+    test("Even length array", () => {
+        TYPED_ARRAYS.forEach(T => {
+            const array = new T([1, 2]);
+            expect(array.toReversed()).toEqual([2, 1]);
+            expect(array).toEqual([1, 2]);
+        });
+
+        BIGINT_TYPED_ARRAYS.forEach(T => {
+            const array = new T([1n, 2n]);
+            expect(array.toReversed()).toEqual([2n, 1n]);
+            expect(array).toEqual([1n, 2n]);
+        });
+    });
+
+    test("Empty array", () => {
+        TYPED_ARRAYS.forEach(T => {
+            const array = new T([]);
+            expect(array.toReversed()).toEqual([]);
+            expect(array).toEqual([]);
+        });
+
+        BIGINT_TYPED_ARRAYS.forEach(T => {
+            const array = new T([]);
+            expect(array.toReversed()).toEqual([]);
+            expect(array).toEqual([]);
+        });
+    });
+});