js 的多态

function Dog(){
    this.bark=null;
}
function Hashiqi(){
    this.bark=function(){
        alert('wuwuwu')
   }
}
function Jingba(){
    this.bark=function(){
        alert('wangwangang');
   }
}
Hashiqi.prototype=Jingba.prototype=new Dog();//原型链的继承
var h=new Hashiqi();
var j=new Jingba();
function test(Dog){
   Dog.bark();
}
test(h);
test(j);