<div id="tab">
 <ul>
 <li><img src="image/pic0.jpg" alt="" /></li>
 <li><img src="image/pic1.jpg" alt="" /></li>
 <li><img src="image/pic2.jpg" alt="" /></li>
 <li><img src="image/pic3.jpg" alt="" /></li>
 </ul>
 <ol>
 <li class="on"></li>
 <li></li>
 <li></li>
 <li></li>
 </ol>
 <a href="javascript:;" rel="external nofollow" rel="external nofollow" class="prev" id="prev"><</a>
 <a href="javascript:;" rel="external nofollow" rel="external nofollow" class="next" id="next">></a> 
</div>

*{margin: 0; padding: 0;}
li{ list-style: none;}
#tab{
 width: 670px;
 height: 240px;
 border: 1px solid #ccc;
 margin: 50px auto;
 position: relative;
}
#tab ul{
 width: 2680px;
 height: 240px;
 position: absolute;
 left: 0;
 top: 0;
 overflow: hidden;
}
#tab ul li{
 float: left;
 width: 670px;
}
#tab ul li img{
 width: 670px;
}
#tab ol{
 width: 80px;
 position: absolute;
 bottom: 10px;
 left: 50%;
 margin-left: -40px;
 overflow: hidden;
}
#tab ol li{
 float: left;
 width: 10px;
 height: 10px;
 background: #ccc;
 border-radius: 50%;
 margin: 5px;
 cursor: pointer;
}
#tab ol .on{
 background: #f00;
}
#tab .prev,#tab .next{
 display: none;
 width: 40px;
 height: 60px;
 background: rgba(0,0,0,.3);
 filter:alpha(opacity:30);
 text-decoration: none;
 text-align: center;
 line-height: 60px;
 font-size: 30px;
 color: #fff;
 position: absolute;
 top: 50%;
 margin-top: -30px;
}
#tab .prev{
 left: 0;
}
#tab .next{
 right: 0;
}

window.onload = function(){
 var oTab = document.getElementById('tab');
 var oUl = oTab.getElementsByTagName('ul')[0];
 var aLi1 = oUl.children;
 var oOl = oTab.getElementsByTagName('ol')[0];
 var aLi2 = oOl.children;
 var prev = document.getElementById('prev');
 var next = document.getElementById('next');
 //設置ul的初始位置
 var iNow = 1; 
 oUl.style.left=-aLi1[0].offsetWidth*iNow+'px';
 //定時器
 var timer = null;

 //克隆第一張圖片 添加在ul的最后面
 var oLi1 = aLi1[0].cloneNode(true);
 //克隆最后一張圖片 添加在ul的最前面
 var oLi2 = aLi1[aLi1.length-1].cloneNode(true);
 oUl.appendChild(oLi1);
 oUl.insertBefore(oLi2,aLi1[0]);
 oUl.style.width = aLi1[0].offsetWidth*aLi1.length+"px";
 //鼠標移入tab: 關閉定時器，左右按鈕顯示
 oTab.onmouseover = function(){
 clearInterval(timer);
 prev.style.display = 'block';
 next.style.display = 'block';
 }
 //鼠標移出tab: 開啟定時器，左右按鈕隱藏
 oTab.onmouseout = function(){
 timer = setInterval(function(){
 toNext();
 },2000);
 prev.style.display = 'none';
 next.style.display = 'none';
 }
 //點擊小圓點
 for(var i=0;i<aLi2.length;i++){
 (function(index){
 aLi2[index].onclick = function(){
 iNow = index+1;
 for(var i=0;i<aLi2.length;i++){
 aLi2[i].className = '';
 }
 aLi2[index].className = 'on';
 animate(oUl,{left: -iNow*aLi1[0].offsetWidth});
 }
 })(i);
 }
 //上一個
 prev.onclick=function(){
 iNow--;
 animate(oUl,{left: -iNow*aLi1[0].offsetWidth},{complete:function(){
 if(iNow == 0){
 iNow = aLi1.length-2;
 oUl.style.left=-aLi1[0].offsetWidth*iNow+'px';
 }
 for(var i=0;i<aLi2.length;i++){
 aLi2[i].className = '';
 }
 aLi2[iNow-1].className = 'on';
 }});
 }
 //下一個
 next.onclick=function(){
 toNext();
 }
 function toNext(){
 iNow++;
 animate(oUl,{left: -iNow*aLi1[0].offsetWidth},{complete:function(){
 if(iNow == aLi1.length-1){
 iNow = 1;
 oUl.style.left=-aLi1[0].offsetWidth*iNow+'px';
 }
 for(var i=0;i<aLi2.length;i++){
 aLi2[i].className = '';
 }
 aLi2[iNow-1].className = 'on';
 }});
 }
 //設置定時器
 timer = setInterval(function(){
 toNext();
 },2000);
}

/*
 * 參數說明:
 * obj: 運動對象
 * json(json形式): 需要修改的屬性
 * options(json形式): 
 * duration: 運動時間
 * easing: 運動方式（勻速、加速、減速）
 * complete: 運動完成后執行的函數
*/
function animate(obj,json,options){
 var options=options || {}; 
 var duration=options.duration || 500; //運動時間,默認值為500ms;
 var easing=options.easing || 'linear'; //運動方式,默認為linear勻速
 var start={};
 var dis={};

 for(var name in json){
 start[name]=parseFloat(getStyle(obj,name)); //起始位置
 dis[name]=json[name]-start[name]; //總距離
 }

 var count=Math.floor(duration/30); //總次數
 var n=0; //次數

 clearInterval(obj.timer);
 obj.timer=setInterval(function(){
 if(n>count){
 clearInterval(obj.timer);
 options.complete && options.complete();
 }else{
 for(var name in json){
 switch(easing){
 //勻速
 case 'linear':
 var a=n/count;
 var cur=start[name]+dis[name]*a; //當前位置
 break;
 //加速
 case 'ease-in':
 var a=n/count;
 var cur=start[name]+dis[name]*a*a*a;
 break;
 //減速
 case 'ease-out':
 var a=1-n/count;
 var cur=start[name]+dis[name]*(1-a*a*a);
 break;
 }
 if(name=='opacity'){
 obj.style.opacity=cur;
 obj.style.filter = 'alpha(opacity='+cur*100+')'; //兼容IE8及以下
 }else{
 obj.style[name]=cur+'px';
 }
 }
 }
 n++;
 },30);
}
//獲取非行間樣式
function getStyle(obj,sName){
 return (obj.currentStyle || getComputedStyle(obj,false))[sName];
}