                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /JS动画效果

帮忙看一看!

<!DOCTYPE html>
<html>
<head>
   <meta charset="UTF-8">
   <title>Document</title>
</head>
<style type="text/css">
*{
   margin:0;
   padding:0;
}
ul,li{
   list-style: none;
}
ul li{
   width: 200px;
   height: 100px;
   background: yellow;
   margin-bottom: 20px;
    border: 10px solid #000;
   font-size:12px;
}
</style>
<script type="text/javascript">
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].onmouseout=function(){
           startMove(this,200);
       }
   }
}
function startMove(obj,iTarget){
   var aLi=document.getElementsByTagName('li');
   clearInterval(obj.timer);
   obj.timer=setInterval(function(){
       var speed=(iTarget-obj.offsetWidth)/10;
       speed=speed>0?Math.ceil(speed):Math.floor(speed);
       if(iTarget==obj.offsetWidth){
           clearInterval(obj.timer);
       }else{

            obj.style.width=parseInt(getStyle(obj,'width'))+speed+'px';
       }
   },30);
}
function getStyle(obj,attr){
   if(obj.currentStyle){
       return obj.currentStyle[attr];
   }else{
       return getComputedStyle(obj,false)[attr];
   }
}
</script>
<body>
   <ul>
       <li >a</li>
       <li>a</li>
       <li>a</li>
   </ul>
</body>
</html>