[jsfm] Freeze the prototype of intrenal and build-in objects

[Hanks10100]

Freeze those objects:

• Internal objects
  • Vm
  • App
  • Element
  • Comment
  • Listener
  • App.prototype
  • Document.prototype
  • Element.prototype
  • Comment.prototype
  • Listener.prototype
• Build-in objects
  • Object
  • Array
  • Object.prototype
  • Array.prototype
  • String.prototype
  • Number.prototype
  • Boolean.prototype
  • Error.prototype
  • Date.prototype
  • RegExp.prototype

Once the object is frozen, there has no chance to unfreeze it.

In addition, because we use strict mode in the js bundle, modify those frozen objects will throw a TypeError.

[Hanks10100]

Notice: Once the prototype is frozen, the instance can't override its properties.

The following code will throw a TypeError.

(function() {
  'use strict';

  function A() {}
  A.prototype.name = 'prototype';
  Object.freeze(A.prototype);

  var a = new A()
  a.name = 'instance';
})()

But you can use Object.defineProperty to override the property.

(function() {
  'use strict';

  function A() {}
  A.prototype.name = 'prototype';
  Object.freeze(A.prototype);

  var a = new A()
  Object.defineProperty(a, 'name', {
    configurable: true,
    enumerable: true,
    writable: true,
    value: 'instance'
  })
})()