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

为什么总是没什么反应？

<!DOCTYPE html>
<html>
<head>
    <title>20160218</title>
    <style type="text/css">
    *{padding: 0;margin:0;}

    ul li{
        width:300px;
        height: 100px;
        background-color: red;
        margin-bottom:20px; 
        border:5px solid green;
    }

    </style>


    <script type="text/javascript">
    window.onload=function(){
        var opp=document.getElementsByTagName("li");
        for (var i=0;i<opp.length;i++){
            opp[i].timer=null;//为什么var opp[i].timer;不行？
            opp[i].onmouseover=function(){
                startMove(this,500);
            }
            opp[i].onmouseout=function(){
                startMove(this,300);
            }
        }
    }
    
   
     function startMove(obj,iTarget){
                clearInterval(obj.timer);
                obj.timer=setInterval(function(){
                    var icur = parseInt(getStyle(obj,"width"));
                    var speed=(iTarget-icur)/8;
                    speed = speed>0?Math.ceil(speed):Math.floor(speed);
                    if(icur==iTarget){
                        clearInterval(obj.timer);
                    }
                    else{
                        obj.style[attr]=icur+speed+'px';
                    }
                },30)
            }
    
    function getStyle(obj,attr){
        if (obj.currentStyle){
           return obj.currentStyle[attr];
        }else{
           return getComputedStyle(obj,false)[attr];
        }
    }

    </script>
</head>
<body>
<ul>
    <li></li>
    <li></li>
    <li></li>
</ul>
</body>
</html>