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