请问我的代码错误哪里！非常感谢！
<!doctype html>
<html>
<head>
<title>多物体运动动画</title>
<meta charset="utf-8">
<style>
*{margin:0;padding: 0px;color: #FFF}
ul,li{list-style: none}
ul li{background: yellow;width: 200px;height: 100px;margin-bottom: 20px}
</style>
<script type="text/javascript">
window.onload=function(){
var lis=document.getElementsByTagName('li');
for(var i=0;i<lis.length;i++){
lis[i].onmouseover=function(){
startMove(this,400)
}
lis[i].onmouseout=function(){
startMove(this,200)
}
}
}
var timer=null;
function startMove(obj,iTarget){
clearInterval(timer);
timer=(function(){
var speed=(iTarget-obj.offsetWidth)/8;
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if(obj.offsetWidth==iTarget){
clearInterval(timer);
}
else{
obj.style.width=obj.offsetWidth+speed+'px';
}
},30)
}
</script>
</head>
<body>
<ul>
<li></li>
<li></li>
<li></li>
</ul>
</div>
</body>
</html>
