LibJS: Implement Object.hasOwn() :^)

This is currently a TC39 Stage 2 proposal, but let's go for it!

https://github.com/tc39/proposal-accessible-object-hasownproperty

I wrote the C++, @linusg found bugs and wrote the test.

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -135,6 +135,7 @@ namespace JS {
     P(globalThis)                            \
     P(groups)                                \
     P(has)                                   \
+    P(hasOwn)                                \
     P(hasOwnProperty)                        \
     P(hypot)                                 \
     P(ignoreCase)                            \

Userland/Libraries/LibJS/Runtime/ObjectConstructor.cpp

@@ -45,6 +45,7 @@ void ObjectConstructor::initialize(GlobalObject& global_object)
     define_native_function(vm.names.values, values, 1, attr);
     define_native_function(vm.names.entries, entries, 1, attr);
     define_native_function(vm.names.create, create, 2, attr);
+    define_native_function(vm.names.hasOwn, has_own, 2, attr);
 }
 
 ObjectConstructor::~ObjectConstructor()
@@ -310,4 +311,15 @@ JS_DEFINE_NATIVE_FUNCTION(ObjectConstructor::create)
     return object;
 }
 
+JS_DEFINE_NATIVE_FUNCTION(ObjectConstructor::has_own)
+{
+    auto* object = vm.argument(0).to_object(global_object);
+    if (vm.exception())
+        return {};
+    auto string_or_symbol = StringOrSymbol::from_value(global_object, vm.argument(1));
+    if (vm.exception())
+        return {};
+    return Value(object->has_own_property(string_or_symbol));
+}
+
 }

Userland/Libraries/LibJS/Runtime/ObjectConstructor.h

@@ -42,6 +42,7 @@ class ObjectConstructor final : public NativeFunction {
     JS_DECLARE_NATIVE_FUNCTION(values);
     JS_DECLARE_NATIVE_FUNCTION(entries);
     JS_DECLARE_NATIVE_FUNCTION(create);
+    JS_DECLARE_NATIVE_FUNCTION(has_own);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Object/Object.hasOwn.js

@@ -0,0 +1,35 @@
+describe("basic functionality", () => {
+    test("length", () => {
+        expect(Object.hasOwn).toHaveLength(2);
+    });
+
+    test("returns true for existent own property", () => {
+        const o = { foo: "bar" };
+        expect(Object.hasOwn(o, "foo")).toBeTrue();
+    });
+
+    test("returns false for non-existent own property", () => {
+        const o = {};
+        expect(Object.hasOwn(o, "foo")).toBeFalse();
+    });
+
+    test("returns false for existent prototype chain property", () => {
+        const o = {};
+        Object.prototype.foo = "bar";
+        expect(Object.hasOwn(o, "foo")).toBeFalse();
+    });
+});
+
+describe("errors", () => {
+    test("null argument", () => {
+        expect(() => {
+            Object.hasOwn(null);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+    });
+
+    test("undefined argument", () => {
+        expect(() => {
+            Object.hasOwn(undefined);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+    });
+});