求助JS链式动画，写在opacity之前的动画可以链式执行，但是一旦有这个属性之后，后面的就不执行了..求助
function startMove(obj,purpose,attr,fn){
var target=0;
clearInterval(obj.timer);
obj.timer=setInterval(function(){
var speed = 0;
if(attr == 'opacity'){
target = Math.round(parseFloat(getStyle(obj,attr))*100);
purpose=purpose*100;
}else{
target=parseInt(getStyle(obj,attr));
}
speed = (purpose-target)/10;
speed = speed>0?Math.ceil(speed):Math.floor(speed);
if(target==purpose){
clearInterval(obj.timer);
if(fn){
fn();
}
}else{
target=target+speed;
if(attr == 'opacity'){
obj.style.opacity=target/100;
}else{
obj.style[attr]=target+'px';
}
}
},30)
}
function getStyle(obj,attr){
if(obj.currentStyle){
return obj.currentStyle[attr];
}else{
return getComputedStyle(obj,false)[attr];
}
}上面是js代码，下面是html代码
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>链式运动</title>
<style type="text/css">
*{margin: 0;padding: 0;}
ul{list-style: none;}
ul li{width:200px;height: 100px;background: yellow;opacity: 0.3;border: 3px solid green;}
</style>
<script type="text/javascript" src="js/script.js"></script>
<script>
window.onload=function(){
var li = document.getElementsByTagName("li")[0];
li.onmouseover=function(){
startMove(li,400,'width',function(){
startMove(li,1,'opacity');
});
}
}
</script>
</head>
<body>
<ul>
<li></li>
</ul>
</body>
</html>这样是可以链式执行的，但是吧上面的顺序换一下就不行了，求帮助
