原型继承的几种方式介绍

原型继承

父级：

    function Parent(name){
        this.name=name;
    }
    Parent.prototype.sayHello=function(){
        console.log("Hello,"+this.name);
    }

1. 原型链继承

   function Kid(){};
   Kid.prototype=new Parent("who");
   
   var k=new Kid();
   console.log(k.name); //who
   console.log(k.sayHello()); //Hello,who

   弊端：创建实例时无法向父级传参

2. 构造继承

   function Kid(name){
       Parent.call(this,name);
   };
   
   var k=new Kid("who");
   console.log(k.name); //who
   console.log(k.sayHello()); //error

   弊端：无法获取父级原型链属性

3. 实例继承

   function Kid(name){
       var p=new Parent(name);
       return p;
   };
   
   var k=new Kid("who");
   console.log(k.name); //who
   console.log(k.sayHello()); //Hello,who

   弊端：实例是父级的实例

4. 拷贝继承

   function Kid(name){
       var p=new Parent(name);
       for(var item in p){
           Kid.prototype[item]=p[item];
       }
   }
   
   var k=new Kid("who");
   console.log(k.name); //who
   console.log(k.sayHello()); //Hello,who

   弊端：太占用内存

5. 组合继承

   function Kid(name){
       Parent.call(this,name);
   }
   Kid.prototype=new Parent();
   
   var k=new Kid("who");
   console.log(k.name); //who
   console.log(k.sayHello()); //Hello,who

   弊端：调用了两次父类构造函数

6. 寄生组合继承

   function Kid(name){
       Parent.call(this,name);
   }
   (function(){
       var p=function(){};
       p.prototype=Parent.prototype;
       Kid.prototype=new p();
   })()

   弊端：写法比较繁琐

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