Add tests for Subclassing the built-in Function Object

test/language/subclassing/Function/instance-length.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.2.4.1
+description: Subclassed Function instances has length and name properties
+info: >
+  19.2.4.1 length
+
+  The value of the length property is an integer that indicates the typical
+  number of arguments expected by the function. However, the language permits
+  the function to be invoked with some other number of arguments. The behaviour
+  of a function when invoked on a number of arguments other than the number
+  specified by its length property depends on the function. This property has
+  the attributes { [[Writable]]: false, [[Enumerable]]: false,
+  [[Configurable]]: true }.
+includes: [propertyHelper.js]
+---*/
+
+class Fn extends Function {}
+
+var fn = new Fn('a', 'b', 'return a + b');
+
+assert.sameValue(fn.length, 2);
+
+verifyNotEnumerable(fn, 'length');
+verifyNotWritable(fn, 'length');
+verifyConfigurable(fn, 'length');

test/language/subclassing/Function/instance-name.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.2.4.2
+description: Subclassed Function instances has length and name properties
+info: >
+  19.2.4.2 name
+
+  The value of the name property is an String that is descriptive of the
+  function. The name has no semantic significance but is typically a variable or
+  property name that is used to refer to the function at its point of definition
+  in ECMAScript code. This property has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+
+  Anonymous functions objects that do not have a contextual name associated with
+  them by this specification do not have a name own property but inherit the
+  name property of %FunctionPrototype%.
+
+  19.2.1.1.1 RuntimeSemantics: CreateDynamicFunction(constructor, newTarget,
+  kind, args)
+
+  ...
+  29. Perform SetFunctionName(F, "anonymous").
+  ...
+includes: [propertyHelper.js]
+---*/
+
+class Fn extends Function {}
+
+var fn = new Fn('a', 'b', 'return a + b');
+
+assert.sameValue(
+  fn.name, 'anonymous',
+  'Dynamic Functions are called anonymous'
+);
+
+verifyNotEnumerable(fn, 'name');
+verifyNotWritable(fn, 'name');
+verifyConfigurable(fn, 'name');

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

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.2.1
+description: Subclassing Function
+info: >
+  19.2.1 The Function Constructor
+
+  ...
+
+  The Function constructor is designed to be subclassable. It may be used as the
+  value of an extends clause of a class definition.
+  ...
+---*/
+
+class Fn extends Function {}
+
+var fn = new Fn('a', 'return a * 2');
+
+assert.sameValue(fn(42), 84);

test/language/subclassing/Function/super-must-be-called.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 19.2.1
+description: >
+  super must be called to initialize Function internal slots
+info: >
+  19.2.1 The Function Constructor
+
+  ...
+
+  The Function constructor is designed to be subclassable. It may be used as the
+  value of an extends clause of a class definition.  Subclass constructors that
+  intend to inherit the specified Function behaviour must include a super call
+  to the Function constructor to create and initialize a subclass instances with
+  the internal slots necessary for built-in function behaviour.
+  ...
+---*/
+
+class Fn extends Function {
+  constructor() {}
+}
+
+assert.throws(ReferenceError, function() {
+  new Fn();
+});
+
+class Fn2 extends Function {
+  constructor() {
+    super();
+  }
+}
+
+var fn = new Fn2();
+assert(fn instanceof Function);