腾讯的一道js面试题（原型）

 1          function Dog(){
 2  2                 this.bark = function(){
 3  3                     alert("汪汪");
 4  4                 }
 5  5             }
 6  6             var huahua = new Dog();
 7  7             huahua.bark();//huahua会汪汪叫
 8  8             
 9  9             function Yellowdog(){
10 10                 this.eat = function(){
11 11                     alert("我会看家");
12 12                 }
13 13             }
14 14             Yellowdog.prototype =new Dog();
15 15             var  yellowdog = new Yellowdog();
16 16             yellowdog.bark();//同伴yellowdog也会汪汪叫
17 17             直接改原型对象的属性
18 18             Yellowdog.prototype.bark = function(){    alert("呜呜");};
19 19             var    newdog = new Yellowdog();
20 20             newdog.bark();//新出生的狗只能呜呜叫