javascript通过apply进析构函数继承

function df(){
var t=new Artist_Tune("Hello","win","lining");
document.writeln(t.toString());
}
function Tune(title,type){
this.title=title;
this.type=type;
this.getTitle=function(){
return (this.title+"   "+this.type);
}
}

function Artist_Tune(title,type,artist){
this.artist=artist;
//this.toString("Artist is"+artist);
Tune.apply(this,arguments);
this.toString=function(){
return "Artist:  "+this.artist+this.getTitle();
}
}

 

window.onload=function(){

Artist_Tune.prototype=new Tune();

}