使用apply方法现实对象继承

function Parent(username)

{

this.username = username;

this.sayHello = function() 

{

alert(this.username);

}

}

function Child(username,pwd)

{

Parent.apply(this,[username]);

        this.pwd = pwd;

       this.sayPwd = function(){

       alert(this.pwd);

}

}

var p = new Parent("admin123");

var c = new Child("admin1","admin12");

p.sayHello ();

c.sayHello ();

c.sayPwd ();