LibJS: Add %TypedArray%.prototype.reduce

Author: https://github.com/IdanHo
Commit: https://github.com/SerenityOS/serenity/commit/23563829389
Pull-request: https://github.com/SerenityOS/serenity/pull/8551
Reviewed-by: https://github.com/linusg
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -37,6 +37,7 @@ void TypedArrayPrototype::initialize(GlobalObject& object)
     define_native_function(vm.names.includes, includes, 1, attr);
     define_native_function(vm.names.indexOf, index_of, 1, attr);
     define_native_function(vm.names.lastIndexOf, last_index_of, 1, attr);
+    define_native_function(vm.names.reduce, reduce, 1, attr);
     define_native_function(vm.names.some, some, 1, attr);
     define_native_function(vm.names.join, join, 1, attr);
     define_native_function(vm.names.keys, keys, 0, attr);
@@ -404,6 +405,44 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::last_index_of)
     return Value(-1);
 }
 
+// 23.2.3.20 %TypedArray%.prototype.reduce ( callbackfn [ , initialValue ] ), https://tc39.es/ecma262/#sec-%typedarray%.prototype.reduce
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::reduce)
+{
+    auto* typed_array = typed_array_from(vm, global_object);
+    if (!typed_array)
+        return {};
+
+    auto length = typed_array->array_length();
+
+    auto* callback_function = callback_from_args(global_object, vm.names.reduce.as_string());
+    if (!callback_function)
+        return {};
+
+    if (length == 0 && vm.argument_count() <= 1) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::ReduceNoInitial);
+        return {};
+    }
+
+    u32 k = 0;
+    Value accumulator;
+    if (vm.argument_count() > 1) {
+        accumulator = vm.argument(1);
+    } else {
+        accumulator = typed_array->get(k);
+        ++k;
+    }
+
+    for (; k < length; ++k) {
+        auto k_value = typed_array->get(k);
+
+        accumulator = vm.call(*callback_function, js_undefined(), accumulator, k_value, Value(k), typed_array);
+        if (vm.exception())
+            return {};
+    }
+
+    return accumulator;
+}
+
 // 23.2.3.25 %TypedArray%.prototype.some ( callbackfn [ , thisArg ] ), https://tc39.es/ecma262/#sec-%typedarray%.prototype.some
 JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::some)
 {

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.h

@@ -34,6 +34,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(includes);
     JS_DECLARE_NATIVE_FUNCTION(index_of);
     JS_DECLARE_NATIVE_FUNCTION(last_index_of);
+    JS_DECLARE_NATIVE_FUNCTION(reduce);
     JS_DECLARE_NATIVE_FUNCTION(some);
     JS_DECLARE_NATIVE_FUNCTION(join);
     JS_DECLARE_NATIVE_FUNCTION(keys);

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

@@ -0,0 +1,39 @@
+const TYPED_ARRAYS = [
+    Uint8Array,
+    Uint8ClampedArray,
+    Uint16Array,
+    Uint32Array,
+    Int8Array,
+    Int16Array,
+    Int32Array,
+    Float32Array,
+    Float64Array,
+];
+
+const BIGINT_TYPED_ARRAYS = [BigUint64Array, BigInt64Array];
+
+test("basic functionality", () => {
+    TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.reduce).toHaveLength(1);
+
+        const typedArray = new T(3);
+        typedArray[0] = 1;
+        typedArray[1] = 2;
+        typedArray[2] = 3;
+
+        expect(typedArray.reduce((accumulator, value) => accumulator + value)).toBe(6);
+        expect(typedArray.reduce((accumulator, value) => accumulator + value, -5)).toBe(1);
+    });
+
+    BIGINT_TYPED_ARRAYS.forEach(T => {
+        expect(T.prototype.reduce).toHaveLength(1);
+
+        const typedArray = new T(3);
+        typedArray[0] = 1n;
+        typedArray[1] = 2n;
+        typedArray[2] = 3n;
+
+        expect(typedArray.reduce((accumulator, value) => accumulator + value)).toBe(6n);
+        expect(typedArray.reduce((accumulator, value) => accumulator + value, -5n)).toBe(1n);
+    });
+});