JavaScript类工厂设计：原型、继承与实现模式详解

  function A(){

  }
  A.prototype = {
    aa:"aa",
    method:function(){
    }
  };
  var a = new A;
  var b = new A;
  console.log(a.aa === b.aa);
  console.log(a.method === b.method)

  function A() {
    var count = 0;
    this.aa = "aa";
    this.method = function() {
      return count;
    }
    this.obj = {}
  }
  A.prototype = {
    aa:"aa",
    method:function(){

    }
  };
  var a = new A;
  var b = new A;
  console.log(a.aa === b.aa);//true 由于aa的值为基本类型，比较值
  console.log(a.obj === b.obj) //false 引用类型，每次进入函数体都要重新创建，因此都不一样。
  console.log(a.method === b.method); //false

  delete a.method;
  delete b.method;
  console.log(a.method === A.prototype.method);//true
  console.log(a.method === b.method); //true

  A.method2 = function(){} //类方法
  var c = new A;
  console.log(c.method2); //undefined

  function A() {};
  A.prototype = {
    aaa : 1
  }
  function B() {};
  B.prototype = A.prototype;
  var b = new B;
  console.log(b.aaa); //=> 1;
  A.prototype.bb = 2;
  console.log(b.bb) //=> 2;

  function extend (des, source) { //des = destination
    for (var property in source)
      des[property] = source[property];
    return des;
  }

  function A() {};
  A.prototype = {
    aa:function(){
      alert(1)
    }
  }
  function bridge() {

  };
  bridge.prototype = A.prototype;

  function B() {}
  B.prototype = new bridge();

  var a = new A;
  var b = new B;

  console.log(a == b) //false 证明成功分开原型
  console.log(A.prototype == B.prototype) //true 子类共享父类的原型方法
  console.log(a.aa === b.aa); //为父类动态添加新的方法
  A.prototype.bb = function () {
    alert(2)
  }
  //true，继承父类的方法
  B.prototype.cc = function (){
    alert(3)
  }
  //false 父类未必有子类的new实例
  console.log(a.cc === b.cc)
  //并且它能够正常通过javascript自带的验证机制instanceof
  console.log(b instanceof A) ;//true
  console.log(b instanceof B) ; //true

  Object.create = function (o) {
    function F() {}
    F.prototype = o;
    return new F();
  }

  function inherit(init, Parent, proto){
    function Son(){
      Parent.apply(this, argument); //先继承父类的特权成员
      init.apply(this, argument); //在执行自己的构造器
    }
  }
  //由于Object.create是我们伪造的，因此避免使用第二个参数
  Son.prototype = Object.create(Parent.prototype,{});
  Son.prototype.toString = Parent.prototype.toString; //处理IEbug
  Son.prototype.valueOf = Parent.prototype.valueOf; //处理IEbug
  Son.prototype.constructor = Son; //确保构造器正常指向，而不是Object
  extend(Son, proto) ;//添加子类的特有的原型成员
  return Son;

  function A(){

  }
  A.prototype = {
    aa:1
  }
  var a = new A;
  console.log(a.aa) ; //=>1

  //将它的所有原型都替换掉
  A.prototype = {
    aa:2
  }
  console.log(a.aa); //=>1

  //于是我们想到每个实例都有一个constructor方法，指向其构造器
  //而构造器上面正好有我们的原型，javascript引擎是不是通过该路线回溯属性呢
  function B(){

  }
  B.prototype = {
    aa:3
  }
  a.constructor = B;
  console.log(a.aa) //1 表示不受影响

  function A(){
    console.log(this.__proto__.aa); //1
    this.aa = 2
  }
  A.prototype = {aa:1}
  var a = new A;
  console.log(a.aa)
  a.__proto__ = {
    aa:3
  }
  console.log(a.aa) //=>2
  delete a. aa; //删除特权属性，暴露原型链上的同名属性
  console.log(a.aa) //=>3

  function A() {}
  A.prototype = {
    aa:1
  }
  function bridge() {}
  bridge.prototype = A.prototype;

  function B(){}
  B.prototype = new bridge();
  B.prototype.constructor = B;
  var b = new B;
  B.prototype.cc = function(){
    alert(3)
  }
  //String.prototype === new String().__proto__ => true
  console.log(B.prototype.__proto__ === A.prototype) //true
  console.log(b.__proto__ == B.prototype); //true 
  console.log(b.__proto__.__proto__ === A.prototype); //true 得到父类的原型对象

  var P = (function(prototype, ownProperty, undefined) {
 return function P(_superclass /* = Object */, definition) {
  // handle the case where no superclass is given
  if (definition === undefined) {
   definition = _superclass;
   _superclass = Object;
  }

  // C is the class to be returned.
  //
  // When called, creates and initializes an instance of C, unless
  // `this` is already an instance of C, then just initializes `this`;
  // either way, returns the instance of C that was initialized.
  //
  // TODO: the Chrome inspector shows all created objects as `C`
  //    rather than `Object`. Setting the .name property seems to
  //    have no effect. Is there a way to override this behavior?
  function C() {
   var self = this instanceof C ? this : new Bare;
   self.init.apply(self, arguments);
   return self;
  }

  // C.Bare is a class with a noop constructor. Its prototype will be
  // the same as C, so that instances of C.Bare are instances of C.
  // `new MyClass.Bare` then creates new instances of C without
  // calling .init().
  function Bare() {}
  C.Bare = Bare;

  // Extend the prototype chain: first use Bare to create an
  // uninitialized instance of the superclass, then set up Bare
  // to create instances of this class.
  var _super = Bare[prototype] = _superclass[prototype];
  var proto = Bare[prototype] = C[prototype] = C.p = new Bare;

  // pre-declaring the iteration variable for the loop below to save
  // a `var` keyword after minification
  var key;

  // set the constructor property on the prototype, for convenience
  proto.constructor = C;

  C.extend = function(def) { return P(C, def); }

  return (C.open = function(def) {
   if (typeof def === 'function') {
    // call the defining function with all the arguments you need
    // extensions captures the return value.
    def = def.call(C, proto, _super, C, _superclass);
   }

   // ...and extend it
   if (typeof def === 'object') {
    for (key in def) {
     if (ownProperty.call(def, key)) {
      proto[key] = def[key];
     }
    }
   }

   // if no init, assume we're inheriting from a non-Pjs class, so
   // default to using the superclass constructor.
   if (!('init' in proto)) proto.init = _superclass;

   return C;
  })(definition);
 }

 // as a minifier optimization, we've closured in a few helper functions
 // and the string 'prototype' (C[p] is much shorter than C.prototype)
})('prototype', ({}).hasOwnProperty);

  var Dog = P (function(proto, superProto){
    proto.init = function(name) { //构造函数
      this.name = name;
    }
    proto.move = function(meters){ //原型方法
      console.log(this.name + " moved " + meters + " m.")
    }
  });
  var a = new Dog("aaa")
  var b = new Dog("bbb"); //无实例变化
  a.move(1);
  b.move(2);

  var Animal = P (function(proto, superProto){
    proto.init = function(name) { //构造函数
      this.name = name;
    }
    proto.move = function(meters){ //原型方法
      console.log(this.name + " moved " + meters + " m.")
    }
  });
  var a = new Animal("aaa")
  var b = new Animal("bbb"); //无实例变化
  a.move(1);
  b.move(2);
  //...............
  var Snake = P (Animal, function(snake, animal){
    snake.init = function(name, eyes){
      animal.init.call(this, arguments); //调运父类构造器
      this.eyes = 2;
    }
    snake.move = function() {
      console.log('slithering...');
      animal.move.call(this, 5); //调运父类同名方法
    }
  });
  var s = new Snake("snake", 1);
  s.move();
  console.log(s.name);
  console.log(s.eyes);

  var Cobra = P (Snake, function(cobra){
    var age = 1;//私有属性
    //这里还可以编写私有方法
    cobra.glow = function(){ //长大
      return age++;
    }
  });
  var c = new Cobra("cobra");
  console.log(c.glow()); //1
  console.log(c.glow()); //2
  console.log(c.glow()); //3