焦点轮播图效果

<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<title>焦点轮播图效果</title>
<style type="text/css">
   *{
       margin: 0;
       padding: 0;
       list-style-type: none;
   }
   .wrap{
       490px;
       height: 170px;
       margin: 100px auto;
       overflow: hidden;
       position: relative;
   }
   .wrap ul{
       position: absolute;
   }
   .wrap li{
       height: 170px;
   }
   .list{
       position: absolute;
       right: 10px;
       bottom: 10px;
   }
   .list li{
       float: left;
       20px;
       height: 20px;
       background-color: #ccc;
       border: 1px solid #666;
       margin-left: 5px;
       color: #000;
       text-align: center;
       line-height: 20px;
       cursor: pointer;
   }
   .list li.on{
       background-color: #E57000;
       color: #fff;
   }
</style>
</head>
<body>
   <div class="wrap" id="wrap">
       <ul class="pic" id="pic">
           <li><img src="http://img.mukewang.com/54111cd9000174cd04900170.jpg" alt="图1" /></li>
           <li><img src="http://img.mukewang.com/54111dac000118af04900170.jpg" alt="图2" /></li>
           <li><img src="http://img.mukewang.com/54111d9c0001998204900170.jpg" alt="图3" /></li>
           <li><img src="http://img.mukewang.com/54111d8a0001f41704900170.jpg" alt="图4" /></li>
           <li><img src="http://img.mukewang.com/54111d7d00018ba604900170.jpg" alt="图5" /></li>
       </ul>
       <ol class="list" id="list">
           <li class="on">1</li>
           <li>2</li>
           <li>3</li>
           <li>4</li>
           <li>5</li>
       </ol>
   </div>
<script type="text/javascript">

   window.onload=function () {
       //获取元素,申明变量
       var wrap=document.getElementById('wrap'),
           pic=document.getElementById('pic'),
           list=document.getElementById('list').getElementsByTagName('li');
       var index=0,
           that=this,
           timer=null;

       //绑定
       function autoPlay(){
           index++;
           if (index>=list.length) {
               index=0;
           }
           qiehuan(index);
       }
       timer=setInterval(autoPlay,2000);
           //鼠标滑过整个容器时停止切换（定时器）
       wrap.onmouseover=function(){
           clearInterval(timer)
       }
       //鼠标离开时，继续切换
       wrap.onmouseout=function(){
           timer=setInterval(autoPlay,2000);
       }

       //遍历所有数字导航，实现滑过切换至对应得图片
       for (var j = 0; j < list.length; j++) {
           list[j].id=j;
           list[j].onmouseover=function(){
               qiehuan(this.id);
               clearInterval(timer);
           }
       }


       function qiehuan(num){
           for (var i = 0; i < list.length; i++) {
               list[i].className="";
           }
           list[num].className="on";
           pic.style.top="-"+num*170+"px";
           num=index;
       }
   }
</script>

</body>
</html>