LibJS: Expose TypedArray.prototype.byteOffset

Author: https://github.com/Lubrsi
Commit: https://github.com/SerenityOS/serenity/commit/4d34802f74c
Pull-request: https://github.com/SerenityOS/serenity/pull/7360
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -59,6 +59,7 @@ namespace JS {
     P(bind)                                  \
     P(buffer)                                \
     P(byteLength)                            \
+    P(byteOffset)                            \
     P(call)                                  \
     P(callee)                                \
     P(cbrt)                                  \

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -24,11 +24,8 @@ void TypedArrayPrototype::initialize(GlobalObject& object)
     // FIXME: This should be an accessor property
     define_native_property(vm.names.length, length_getter, nullptr, Attribute::Configurable);
     define_native_property(vm.names.buffer, buffer_getter, nullptr, Attribute::Configurable);
-<<<<<<< HEAD
-=======
     define_native_property(vm.names.byteLength, byte_length_getter, nullptr, Attribute::Configurable);
-    define_native_property(vm.names.BYTES_PER_ELEMENT, bytes_per_element_getter, nullptr, 0); // FIXME: This should just be a normal property and not a getter.
->>>>>>> 6be44bc62... LibJS: Expose TypedArray.prototype.byteLength
+    define_native_property(vm.names.byteOffset, byte_offset_getter, nullptr, Attribute::Configurable);
     define_native_function(vm.names.at, at, 1, attr);
 }
 
@@ -102,4 +99,16 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::byte_length_getter)
     return Value(typed_array->byte_length());
 }
 
+// https://tc39.es/ecma262/#sec-get-%typedarray%.prototype.byteoffset
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::byte_offset_getter)
+{
+    auto typed_array = typed_array_from(vm, global_object);
+    if (!typed_array)
+        return {};
+    auto* array_buffer = typed_array->viewed_array_buffer();
+    VERIFY(array_buffer);
+    // FIXME: If array_buffer is detached, return 0.
+    return Value(typed_array->byte_offset());
+}
+
 }

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.h

@@ -22,6 +22,7 @@ private:
     JS_DECLARE_NATIVE_GETTER(length_getter);
     JS_DECLARE_NATIVE_GETTER(buffer_getter);
     JS_DECLARE_NATIVE_GETTER(byte_length_getter);
+    JS_DECLARE_NATIVE_GETTER(byte_offset_getter);
 
     JS_DECLARE_NATIVE_FUNCTION(at);
 };

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

@@ -0,0 +1,28 @@
+// Update when more typed arrays get added
+const TYPED_ARRAYS = [
+    Uint8Array,
+    Uint16Array,
+    Uint32Array,
+    Int8Array,
+    Int16Array,
+    Int32Array,
+    Float32Array,
+    Float64Array,
+];
+
+test("basic functionality", () => {
+    TYPED_ARRAYS.forEach(T => {
+        const typedArray = new T([1, 2, 3]);
+        expect(Object.hasOwn(typedArray, "byteOffset")).toBeFalse();
+        expect(typedArray.byteOffset).toBe(0);
+        expect(typedArray.length).toBe(3);
+
+        const buffer = typedArray.buffer;
+
+        const arrayFromOffset = new T(buffer, T.BYTES_PER_ELEMENT);
+        expect(arrayFromOffset.byteOffset).toBe(T.BYTES_PER_ELEMENT);
+        expect(arrayFromOffset.length).toBe(2);
+        expect(arrayFromOffset[0]).toBe(2);
+        expect(arrayFromOffset[1]).toBe(3);
+    });
+});