js实现无缝滚动图

   ul, li { padding: 0; margin: 0; }

   li { list-style: none; }

   .box {

   width: 800px;

   height: 450px;

   margin: 50px auto;

   overflow: hidden;

   position: relative;

   }

   .box span {

   width: 40px;

   height: 60px;  

   display: block;

   position: absolute;

   top: 225px;

   margin-top: -20px;

   cursor: pointer;

   z-index: 1;

   }

   .box #left {

 background: url('http://cdn.attach.qdfuns.com/notes/pics/201701/14/042311cbd7gbjd7sggkd2b.png') no-repeat;

 left: 0;

   }

   .box #right {

   background: url('http://cdn.attach.qdfuns.com/notes/pics/201701/14/042241w8z4hx4m4pjhyjzs.png') no-repeat;

   right: 0;

   }

   #ad {

   width: 4000px;

   height: 450px;

   position: absolute;

   }

   #ad li {

 float: left;

   }

   window.onload = function(){

   var ad = document.getElementById("ad");

   var timer = null;//管理定时器

   var leader = 0;

    //1秒之后再开启定时器

    timer = setTimeout(function(){

     timer = setInterval(autoAd,30);

    },1000);

   //开启定时器

   function autoAd(){  

   leader -=5;

   leader<=-3200?leader = 0:leader;

   ad.style.left = leader +"px";

   }

   //鼠标划入 关闭定时器

   ad.onmouseover = function() {  

   clearInterval(timer);

   }

   //鼠标离开 开启定时器

   ad.onmouseout = function(){

   timer = setInterval(autoAd,20);

   }

   }