为什么我的鼠标放上去都没用反应 啊？代码如下，哪里错了，求大神指点
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{margin:0px;padding:0px;}
ul,li{
list-style:none;
}
ul li{
width:200px;
height:100px;
background:yellow;
margin-bottom:20px;
}
</style>
<script>
window.onload=function(){
var ali=document.getElementsByTagName('li');
for(var i=0;i<ali.length;i++)
ali[i].timer=null;
ali[i].onmouseOver=function(){
startMove(this,400);
}
ali[i].onmousOout=function(){
startMove(this,200)
}
}
//var timer=null;
function startMove(obj,iTarget){
clearInterval(obj.timer);
obj.timer=setInterval(function(){
var speed=(iTarget-obj.offsetWidth)/8;
alert(speed)
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if(obj.offsetWidth==iTarget){
clearInterval(obj.timer);
}
else{
obj.style.width=obj.offsetWidth+speed+'px';
}
},30)
}
</script>
</head>
<body>
<ul>
<li></li>
<li></li>
<li></li>
<li></li>
</ul>
</body>
</html>
