LibJS: Expose TypedArray.prototype.buffer

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -57,6 +57,7 @@ namespace JS {
     P(atan2)                                 \
     P(atanh)                                 \
     P(bind)                                  \
+    P(buffer)                                \
     P(byteLength)                            \
     P(call)                                  \
     P(callee)                                \

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.cpp

@@ -23,6 +23,7 @@ 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);
     define_native_function(vm.names.at, at, 1, attr);
 }
 
@@ -73,4 +74,15 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::at)
     return typed_array->get(index.value());
 }
 
+// https://tc39.es/ecma262/#sec-get-%typedarray%.prototype.buffer
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::buffer_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);
+    return Value(array_buffer);
+}
+
 }

Userland/Libraries/LibJS/Runtime/TypedArrayPrototype.h

@@ -20,6 +20,7 @@ public:
 
 private:
     JS_DECLARE_NATIVE_GETTER(length_getter);
+    JS_DECLARE_NATIVE_GETTER(buffer_getter);
 
     JS_DECLARE_NATIVE_FUNCTION(at);
 };

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

@@ -0,0 +1,31 @@
+// 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();
+
+        const buffer = typedArray.buffer;
+        expect(buffer).toBeInstanceOf(ArrayBuffer);
+        expect(buffer.byteLength).toBe(typedArray.byteLength);
+        expect(buffer.byteLength).toBe(typedArray.length * typedArray.BYTES_PER_ELEMENT);
+
+        const arrayFromBuffer = new T(buffer);
+        expect(arrayFromBuffer.length).toBe(typedArray.length);
+        expect(arrayFromBuffer.byteLength).toBe(typedArray.byteLength);
+        expect(arrayFromBuffer.byteOffset).toBe(typedArray.byteOffset);
+        expect(arrayFromBuffer[0]).toBe(typedArray[0]);
+        expect(arrayFromBuffer[1]).toBe(typedArray[1]);
+        expect(arrayFromBuffer[2]).toBe(typedArray[2]);
+    });
+});