在网上搜了一堆，不是包含的框架太多，就是太简单，所以我综合了一下，写一个目前我觉得最通俗易懂的下拉列表实现。利用absolute布局，设置div的left和top来实现下拉列表，在开发时，发现在火狐中设置td的position为absolute是无效的，所以改用li实现。
效果图：
前台代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>js下拉菜单实现</title>
<style>
body{font-size:12px; background:#f3f4f4 url(bg.gif) repeat-x;font-family:Tahoma;}
*{margin:0px;padding:0px;}
.menu
{
text-align:center;
margin:auto;
margin-top:50px;
border-bottom:3px solid #E10001;
width:500px;
height:24px;
}
.menu ul{
list-style:none;
}
.menu .top
{
float:left;
text-align:center;
background-image:url('nav_bg2.gif');
width:87px;
position:relative;
line-height:24px;
height:24px;
margin-left:2px;
}
.menu .top a
{
color:black;
text-decoration:none;
font-size:18px;
}
.menu .top a:hover
{
color:Red;
}
.menu .dropdown{
position:relative;
}
.menu .dropdown a
{
display:block;
}
.menu .dropdowndiv{
display:none;
color:black;
position:absolute;
left:0px;
top:20px;
border:1px solid #64ace9;
background-color:White;
text-align:left;
z-index:999999;
}
/*
利用h2做偏移挡住原先的一级标题
*/
.menu .dropdowndiv h2
{
background-color:#fff;
border:1px solid #64ace9;
position:absolute;
top:-22px;
left:-1px;
border-bottom:0px;
font-size:100%;
font-weight:normal;
text-align:center;
}
.menu .dropdowndiv h2 a
{
color:Black;
font-size:18px;
width:87px;
}
.menu .dropdowndiv ul
{
list-style-image:none;
}
.menu .dropdowndiv li
{
list-style:none;
padding-left:10px;
padding-top:4px;
margin-left:4px;
background-repeat:no-repeat;
background-position:left center;
height:25px;
line-height:25px;
text-align:left;
z-index:999999;
}
.menu .dropdowndiv li a
{
color:black;
font-size:14px;
}
</style>
<script src="jquery-1.4.1.min.js"></script>
<script>
$(document).ready(function () {
$(".dropdown").mouseover(function () {
var ddv = $(this).find(".dropdowndiv");
$(ddv).show();
});
$(".dropdown").mouseout(function () {
var ddv = $(this).find(".dropdowndiv");
$(ddv).hide();
});
});
</script>
</head>
<body>
<div class="menu">
<ul>
<li class="top"><a href="#" target="_self">首页</a></li>
<li class="top dropdown">
<a href="#" target="_self">菜单1</a>
<div class="dropdowndiv" style="width:120px;">
<h2><a href="#" target="_self">菜单1</a></h2>
<ul>
<li><a href="#">菜单1-1</a></li>
<li><a href="#">菜单1-2</a></li>
<li><a href="#">菜单1-3</a></li>
</ul>
</div>
</li>
<li class="top"><a href="#" target="_self">菜单2</a></td>
<li class="top dropdown"><!--火狐不支持td的position-->
<a href="#" target="_self">菜单3</a>
<div class="dropdowndiv" style="width:120px;">
<h2><a href="#" target="_self">菜单3</a></h2>
<ul>
<li><a href="#">菜单3-1</a></li>
<li><a href="#">菜单3-2</a></li>
<li><a href="#">菜单3-3</a></li>
</ul>
</div>
</li>
</ul>
</div>
</body>
</html>