求帮忙 看看哪里错了

window.onload=function(){

var aLi=document.getElementsByTagName('li');

    for(var i=0;i<aLi.length;i++){ 

aLi[i].onmouseover=function(){

startMove(this,400);

}

aLi[i].onmouseout=function(){

startMove(this,200);

}

}

}

var timer=null;

function startMove(obj,iTarget){

clearInterval(timer);

timer=setInterval(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)

}