JavaScript无缝滚动

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        *{margin:0;
        padding: 0;
        }
        #div1{
            width:1320px;
            height:213px;
            margin:100px auto;
            position: relative;
            background: red;
            overflow: hidden;
        }
        #div1 ul{
            position: absolute;
            left:0;
            top:0;
        }
        #div1 ul li{
        float: left;
        width:330px;
        height:213px;
        list-style: none;
        }
    </style>
    <script>
        window.onload=function(){
            var oDiv=document.getElementById('div1');
            var oUl=oDiv.getElementsByTagName('ul')[0]
            var aLi=oUl.getElementsByTagName('li');
            var speed=2;

            oUl.innerHTML=oUl.innerHTML+oUl.innerHTML;
            oUl.style.width=aLi[0].offsetWidth*aLi.length+'px';

            function move(){
                    if(oUl.offsetLeft<-oUl.offsetWidth/2){
                        oUl.style.left='0';
                    }
                    if(oUl.offsetLeft>0){
                        oUl.style.left=-oUl.offsetWidth/2+'px';
                    }
                    oUl.style.left=oUl.offsetLeft-speed+'px';
                }

            var timer=setInterval(move,30);

            oDiv.onmouseover=function(){
                clearInterval(timer);
            };
            oDiv.onmouseout=function(){
                timer=setInterval(move,30);
            }

        }
    </script>
</head>
<body>
<div id="div1">
    <ul>
        <li><img src="img/1.jpg"/></li>
        <li><img src="img/2.jpg"/></li>
        <li><img src="img/3.jpg"/></li>
        <li><img src="img/4.jpg"/></li>
    </ul>
</div>
</body>
</html>

JavaScript无缝滚动