js组合式继承

组合式继承是比较经典的继承,但是也有比较严重的缺点就是连两次调用了父类的构造函数。

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Title</title>
 6 </head>
 7 <body>
 8 <script>
 9     function SuperType(name){
10         this.name=name;
11         this.colors=["red","blue","green"];
12     }
13     SuperType.prototype.sayName=function(){
14         console.log(this.name);
15     }
16     function SubType(name,age){
17         SuperType.call(this,name);//此时会执行SuperType函数,其中的this就会指向SubType,第二次调用父类
18         this.age=age;
19     }
20     SubType.prototype=new SuperType();//第一次调用父类
21     SubType.prototype.constructor=SubType;
22     SubType.prototype.sayAge=function(){
23         console.log(this.age);
24     }
25     var instance1=new SubType("zxf",24);
26     console.log(SubType.prototype);
27     instance1.colors.push("black");
28     console.log(instance1.colors);//["red","blue","green","black"]
29     instance1.sayName();//"zxf"
30     instance1.sayAge();//24
31     delete instance1.colors;
32     var instance2=new SubType("jay",36);
33     console.log(instance2.colors);//["red","blue","green"]
34     instance2.sayName();//"jay"
35     instance2.sayAge();//36
36     /*
37     * 此方法有弊端,就是 SubType.prototype=new SuperType();这句话会导致子类的原型指向父类,并且会有父类的属性name,colors,
38     * 继承这些属性其实在子类中用SuperType.call()已经实现了,这句话会让子类的实例拥有colors,name属性,并且会覆盖子类原型上的name,colors属性,就是上面一行提到的
39     * 所以这是个弊端,可以用寄生组合式继承来避免
40     * */
41 </script>
42 </body>
43 </html>
View Code

 

posted @ 2017-05-19 14:42  fantasy-zxf  阅读(422)  评论(0编辑  收藏  举报