javascript实现左右控制无缝滚动

<</SPAN>html>
<</SPAN>head lang="en">
    <</SPAN>meta charset="UTF-8">
    <</SPAN>title>无缝滚动</</SPAN>title>
    <</SPAN>script src="js/0010.js"></</SPAN>script>
    <</SPAN>link rel="stylesheet" type="text/css" href="css/0010.css" />
</</SPAN>head>
<</SPAN>body>
   <</SPAN>a href="javascript:">向左走</</SPAN>a>
   <</SPAN>a href="javascript:">向右走</</SPAN>a>
   <</SPAN>div id="div1">
       <</SPAN>ul>
           <</SPAN>li><</SPAN>img src="image/1.jpg"></</SPAN>li>
           <</SPAN>li><</SPAN>img src="image/2.jpg"></</SPAN>li>
           <</SPAN>li><</SPAN>img src="image/3.jpg"></</SPAN>li>
           <</SPAN>li><</SPAN>img src="image/4.jpg"></</SPAN>li>
       </</SPAN>ul>
   </</SPAN>div>
</</SPAN>body>
</</SPAN>html>

*{
    margin:0;
    padding: 0;
}
#div1{
    overflow: hidden;
    background: blue;
    position: relative;
    width: 600px;
    height: 150px;
    margin:100px auto;
}
#div1 ul{
    position: absolute;
    left: 0px;
    top: 0px;
    list-style: none;
}
#div1 ul li{
    float: left;
}
#div1 ul li img{
    width:150px;
    height:150px;
}

window.onload=function(){
    var oDiv=document.getElementById('div1');
    var oUl=oDiv.getElementsByTagName('ul')[0];
    var aLi=oUl.getElementsByTagName('li');
    var timer=null;
    var speed=2;//控制滚动速度以及方向
    oUl.innerHTML=oUl.innerHTML+oUl.innerHTML;
    oUl.style.width=aLi[0].offsetWidth*aLi.length+'px';
    timer=setInterval(move,30);
    oDiv.onmouseover=function(){//鼠标移入暂定
        clearInterval(timer);
    };
    oDiv.onmouseout=function(){//鼠标移出继续滚动
        timer=setInterval(move,30);
    }
    document.getElementsByTagName('a')[0].onclick=function(){
        speed=-2;
    }
    document.getElementsByTagName('a')[1].onclick=function(){
        speed=2;
    }
    function move(){//图片滚动
        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';
    }
}