说明：
设置一个标识数字置为0，写一个每过几秒标识+1,执行切换效果的函数，然后执行。
当标识超过当前选项卡长度让标识置为0。
在鼠标移到选项卡的时候关闭定时器，鼠标移走的时候打开定时器。
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<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312" />
<title>无标题文档</title>
<style>
body,ul,li{
margin:0;
padding:0;
font:12px/1.5 arial;
}
ul,li{
list-style:none;
}
.wrap{
width:500px;
margin:20px auto;
}
.hide{
display:none;
}
#tab_t{
height:25px;
border-bottom:1px solid #ccc;
}
#tab_t li{
float:left;
width:80px;
height:24px;
line-height:24px;
margin:0 4px;
text-align:center;
border:1px solid #ccc;
border-bottom:none;
background:#f5f5f5;
cursor:pointer
}
#tab_t .act{
position:relative;
height:25px;
margin-bottom:-1px;
background:#fff;
}
#tab_c{
border:1px solid #ccc;
border-top:none;
padding:20px;
}
</style>
<script>
window.onload = function(){
tab("tab_t","li","tab_c","div","onmouseover")
function tab(tab_t,tab_t_tag,tab_c,tag_c_tag,evt){
var tab_t = document.getElementById(tab_t);
var tab_t_li = tab_t.getElementsByTagName(tab_t_tag);
var tab_c = document.getElementById(tab_c);
var tab_c_li = tab_c.getElementsByTagName(tag_c_tag);
var len = tab_t_li.length;
var i=0;
var timer = null;
var num=0;
for(i=0; i<len; i++){
tab_t_li[i].index = i;
tab_t_li[i][evt] = function(){
clearInterval(timer);
num = this.index;
tab_change()
}
tab_t_li[i].onmouseout = function(){
autoplay();
}
}
function tab_change(){
for(i=0; i<len; i++){
tab_t_li[i].className = '';
tab_c_li[i].className = 'hide';
}
tab_t_li[num].className = 'act';
tab_c_li[num].className = '';
}
function autoplay(){
timer = setInterval(function(){
num++;
if(num>=len) num=0;
tab_change();
},1000);
}
autoplay();
}
}
</script>
</head>
<body>
<div class="wrap">
<ul id="tab_t">
<li class="act">选择1</li>
<li>选择2</li>
<li>选择3</li>
<li>选择4</li>
</ul>
<div id="tab_c">
<div>内容1</div>
<div class="hide">内容2</div>
<div class="hide">内容3</div>
<div class="hide">内容4</div>
</div>
</div>
</body>
</html>
