JS 类的问题

<html xmlns="http://www.w3.org/1999/xhtml" >

<head>

    <title>无标题页</title>

        <style type="text/css">

.game{ width:80px;height:110px;border:1px solid #BAD1FC; background:url(hhh.gif);}

.game head{}

.game foot{}

        </style>

</head>

<body>

<script type="text/jscript">

function person(id,name,x,y){

this._id=id;

this.name=name;

this._x=x;

this._y=y;

this._bl=1;

this._m=1;

}

person.prototype.getdiv =function(){



    if(document.getElementById(this._id))

        {

        this._div=document.getElementById(this._id);

        } else

        {

        try{

            this._div=document.createElement("div");

            this._div.id=this._id;

            document.body.appendChild(this._div);

            this._div_h=document.createElement("div");

            this._div_f=document.createElement("div");

            this._div.appendChild(this._div_h);

            this._div.appendChild(this._div_f);

            this._div.style.position="absolute";

            this._div.style.top=this._y+"px";

            this._div.style.left=this._x+"px";

            this._div.setAttribute("class","game");

            //this._div.innerHTML="success";

            this._div_h.setAttribute("class","head");

            this._div_f.setAttribute("class","foot");

            this._div_h.innerHTML=this.name+this._id;

        }catch(e){return false;}

    }

}

var a= new person('eric','shmily','88','400');

a.getdiv();

</script>







</body>

</html>