Add tests for Subclassing the built-in Object

test/language/subclassing/Object/constructor-return-undefined-throws.js

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+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 9.2.2
+description: Throws a ReferenceError if constructor result is undefined
+info: >
+  9.2.2 [[Construct]] ( argumentsList, newTarget)
+
+  ...
+  11. Let result be OrdinaryCallEvaluateBody(F, argumentsList).
+  ...
+  13. If result.[[type]] is return, then
+    a. If Type(result.[[value]]) is Object, return
+    NormalCompletion(result.[[value]]).
+    ...
+    c. If result.[[value]] is not undefined, throw a TypeError exception.
+  ...
+  15. Return envRec.GetThisBinding().
+
+  8.1.1.3.4 GetThisBinding ()
+
+  ...
+  3. If envRec.[[thisBindingStatus]] is "uninitialized", throw a ReferenceError
+  exception.
+  ...
+
+---*/
+
+class Obj extends Object {
+  constructor() {
+    return undefined;
+  }
+}
+
+class Obj2 extends Object {
+  constructor() {}
+}
+
+assert.throws(ReferenceError, function() {
+  new Obj();
+});
+
+assert.throws(ReferenceError, function() {
+  new Obj2();
+});

test/language/subclassing/Object/constructor-returns-non-object.js

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+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 9.2.2
+description: The Type of the return value must be an Object
+info: >
+  9.2.2 [[Construct]] ( argumentsList, newTarget)
+
+  ...
+  11. Let result be OrdinaryCallEvaluateBody(F, argumentsList).
+  ...
+  13. If result.[[type]] is return, then
+    a. If Type(result.[[value]]) is Object, return
+    NormalCompletion(result.[[value]]).
+    ...
+    c. If result.[[value]] is not undefined, throw a TypeError exception.
+  ...
+
+  6.1.7.2 Object Internal Methods and Internal Slots
+
+  ...
+  If any specified use of an internal method of an exotic object is not
+  supported by an implementation, that usage must throw a TypeError exception
+  when attempted.
+
+  6.1.7.3 Invariants of the Essential Internal Methods
+
+  [[Construct]] ( )
+    - The Type of the return value must be Object.
+---*/
+
+class Obj extends Object {
+  constructor() {
+    return 42;
+  }
+}
+
+assert.throws(TypeError, function() {
+  var obj = new Obj();
+});

test/language/subclassing/Object/regular-subclassing.js

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+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.1.1
+description: Subclassing Object
+info: >
+  19.1.1 The Object Constructor
+
+  The Object constructor is designed to be subclassable. It may be used as the
+  value of an extends clause of a class definition.
+---*/
+
+class Obj extends Object {}
+
+var obj = new Obj();
+
+assert.notSameValue(
+  Object.getPrototypeOf(obj), Object.prototype,
+  'returns the class prototype'
+);

test/language/subclassing/Object/replacing-prototype.js

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+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.1.1
+description: Subclassing Object replacing a prototype method
+info: >
+  19.1.1 The Object Constructor
+
+  The Object constructor is designed to be subclassable. It may be used as the
+  value of an extends clause of a class definition.
+---*/
+
+class Obj extends Object {
+  valueOf() {
+    return 42;
+  }
+}
+
+var obj = new Obj();
+
+assert.sameValue(obj.valueOf(), 42, 'Replaces prototype');