这个问题刚开始的时候挺纠结的，怎么从getelementsByTagName（）获得，用index和this即可做到，还有的应用到数组的遍历具体看下面的代码吧！
HTML和js代码
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>TAB切换</title>
<link href="css/tab.css" rel="stylesheet">
</head>
<body>
<div class="div_bg">
<ul id="bg">
<li id="bg1" class="nobg" onmouseover="tab()"><a class="white">小说</a></li>
<li id="bg2" class="nobg" onmouseover="tab()"><a class="white">非小说</a></li>
<li id="bg3" class="nobg"><a class="white">少儿</a></li>
</ul>
<div id="book1">
<a href="#" target=_blank>1.时间旅行者的妻子</a><br>
<a href="#" target=_blank>2.女心理师（下）</a><br>
<a href="#" target=_blank>3.鬼吹灯之精绝古城</a><br>
<a href="#" target=_blank>4.女心理师（上）</a><br>
<a href="#" target=_blank>5.小时候</a><br>
<a href="#" target=_blank>6.追风筝的人</a><br>
<a href="#" target=_blank>7.盗墓笔记2</a><br>
<a href="#" target=_blank>8.输赢</a>
</div>
<div id="book2">
<a href="#" target=_blank>1.人生若只如初见</a><br>
<a href="#" target=_blank>2.高效能人士的七个..</a><br>
<a href="#" target=_blank>3.求医不如求己</a><br>
<a href="#" target=_blank>4.人体使用手册</a><br>
<a href="#" target=_blank>5.孩子，把你的手给我</a><br>
<a href="#" target=_blank>6.别笑！我是英文单词书</a><br>
<a href="#" target=_blank>7.人体经络使用手册</a><br>
<a href="#" target=_blank>8.股市稳赚</a>
</div>
<div id="book3">
<a href="#" target=_blank>1.斯凯瑞金色童书・..</a><br>
<a href="#" target=_blank>2.哈利・波特与“混..</a><br>
<a href="#" target=_blank>3.不一样的卡梅拉（..</a><br>
<a href="#" target=_blank>4.它们是怎么来的</a><br>
<a href="#" target=_blank>5.五・三班的坏小子..</a><br>
<a href="#" target=_blank>6.男生日记</a><br>
<a href="#" target=_blank>7.哈利・波特与魔法石</a><br>
<a href="#" target=_blank>8.噼里啪啦丛书(全7册)</a>
</div>
</div>
</body>
<script type="text/javascript">
window.onload=function(){
var list = document.getElementsByTagName("li");
for(var i=0;i<list.length;i++){
list[i].index=i;
list[i].onmousemove=function(){
//获得当前元素的下表
var index = this.index;
//给每一个元素恢复原始
for(var i=0;i<3;i++){
document.getElementById("bg"+(i+1)).className="nobg";
document.getElementById("book"+(i+1)).style.display="none";
}
//对选择的元素添加样式
document.getElementById("bg"+(index+1)).className="bg";
document.getElementById("book"+(index+1)).style.display="block";
}
}
}
</script>
</html>
css代码
*{
margin:0;
padding: 0;
font-family: "Arial", "微软雅黑";
font-size: 12px;
line-height: 23px;
}
ul,li{list-style: none;}
li{float: left; margin-right: 1px;}
.div_bg{
background-image:url(../images/bg.jpg);
background-repeat:no-repeat;
width:169px;
height:290px;
margin-top: 0px;
margin-right: auto;
margin-bottom: 0px;
margin-left: auto;
padding: 50px 0 0 15px;
position: relative;
}
.div_bg div{
clear: both; padding-top: 10px;}
.white{font-size:12px;
color:#FFFFFF;
padding-top:2px;
cursor:pointer;
}
.white:hover{font-size:12px;
color:#FFFFFF;
padding-top:2px;
cursor:pointer;
}
a {
color: #06329b;text-decoration: none;line-height:24px;
}
a:hover {
color: #cc0000;text-decoration: none;line-height:24px;
}
.bg{background-image:url(../images/menu1.gif);
background-repeat:no-repeat;
height:23px;
width:47px;
text-align:center;}
.nobg{background-image:url(../images/menu2.gif);
background-repeat:no-repeat;
height:23px;
width:47px;
text-align:center;
}
#book2,#book3{
display: none;
}
.div_bg div{
position: absolute;
top: 80px;
}