prototype 原型对象继承

a继承b

<script>

function b(){
this.bname = "99";
}

function a(){
this.aname = "5";
}

a.prototype = new b();
a.prototype.cname = "66";

var a = new a();

console.log(a.aname); //5
console.log(a.bname); //99
console.log(a.cname); //66

</script>