原型繼承的幾種方式介紹

原型繼承

父級：

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

1. #原型鏈繼承

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

   弊端：建立實例時無法向父級傳參詞

2. 建構繼承

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

   弊端：無法取得父級原型鏈屬性

3. 實例繼承

   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：實例是父級的實例

4. 拷貝繼承

   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：太佔用記憶體

5. 組合繼承

   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：呼叫了兩次父類別建構函數

6. 寄生組合繼承

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

   弊端：寫法比較繁瑣

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