js继承

JS继承
（１）构造函数法
 

 function Parent(){
    this.name = "parentname";
  }
  function Child(age,address){
      Parent.call(this,arguments);
      this.age = age;
      this.address = address;
  }
  var child = new Child();
  console.log(child.name);

（２） 原型继承法
　　

　function Parent(){
    this.name = "parentname";
  }
  function Child(age,address){
      this.age = age;
      this.address = address;
  }
  Child.prototype = new Parent();//缺点是如果Parent比较大会浪费内存
  var child = new Child();
  console.log(child.name);//parentname

（３）直接继承prototype
 

function Parent(name){
    this.name = name;
  }
  Parent.prototype.name = "prototypename";
  function Child(age,address){
      Parent.call(this,"childname");//继承父类中的属性
      this.age = age;
      this.address = address;
  }
  Child.prototype = Parent.prototype;//缺点是Child和Parent的原型都指向了同一个对象，那么对任何一个的修改都会影响另一个
  var child = new Child();
  console.log(child.name);//childname

（４）利用空对象做为中介
 

function Parent(){
    this.name = "parentname";
  }
  function Child(age,address){
      this.age = age;
      this.address = address;
  }
  var F = function(){};
  F.prototype = Parent.prototype;
  Child.prototype = new F();
  Child.prototype.constructor = Child;
  var child = new Child();
  console.log(child.name);

上述抽象成方法如下：

function extend(child,parent){
    var F = new Function();
     F.prototype = parent.prototype;
    child.prototype = new F();
    child.prototype.constructor = child;
    child.uber = parent.prototype.constructor;
 }
 function Parent(){
    this.name = "parentname";
  }
 function Child(age,address){
      Child.uber.call(this,arguments);
      this.age = age;
      this.address = address;
  }
 extend(Child,Parent);
 var child = new Child();
 console.log(child.name);

(5) 拷贝继承
 

function Parent(){
   this.name = "parentname";
 }
 Parent.prototype.getName=function(){
      alert("prototypename");
 };
 function Child(age,address){
      this.age = age;
      this.address = address;
  }
 function extend2(child,parent){//拷贝原型中的属性
    var P = parent.prototype;
    var C = child.prototype;
     for (var i in P){
    C[i] = P[i];
    }
    C.uber = P;
 }
 extend2(Child,Parent);
 var child = new Child();
 console.log(child.getName());
 console.log(child.name);//underfinded