使用apply方法实现javascript中的对象继承

<script type="text/javascript"> 
//使用apply方法实现对象继承 function Parent(username) { 
this.username = username; 
this.sayHello = function() { 
alert(this.username); 
} 
} 
function Child(username, password) { 
Parent.apply(this, new Array(username)); 
//和下面一样 
//Parent.apply(this, [username]); 
this.password = password; 
this.sayWorld = function() { 
alert(this.password); 
} 
} 
var parent = new Parent("zhangsan"); 
var child = new Child("lisi", "123"); 
parent.sayHello(); 
child.sayHello(); 
child.sayWorld(); 
</script>