例子，js下拉菜单。
<!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 runat="server">
<title>javascript下拉菜单-www.yuju100.com</title>
<style type="text/css">
* {
padding:0;
margin:0;
}
body {
font-family:verdana, sans-serif;
font-size:small;
}
#navigation ,#navigation li ul {
list-style-type:none;
}
#navigation {
margin:20px;
}
#navigation li {
float:left;
text-align:center;
position:relative;
}
#navigation li a:link, #navigation li a:visited {
display:block;
text-decoration:none;
color:#000;
width:120px;
height:40px;
line-height:40px;
border:1px solid #fff;
border-width:1px 1px 0 0;
background:#c5dbf2;
text-align:center;
}
#navigation li a:hover {
color:#fff;
background:#2687eb;
}
#navigation li ul {
display:none;
position:absolute;
top:40px;
left:0;
margin-top:1px;
width:120px;
}
#navigation li ul li a:hover {
color:#fff;
background:#6b839c;
}
</style>
<script type="text/javascript">
function displaySubMenu(li) {
var subMenu = li.getElementsByTagName("ul")[0];
subMenu.style.display = "block";
}
function hideSubMenu(li) {
var subMenu = li.getElementsByTagName("ul")[0];
subMenu.style.display = "none";
}
</script>
</head>
<body>
<ul id="navigation">
<！--加上js 鼠标事件-->
<li onmouseover="displaySubMenu(this)" onmouseout="hideSubMenu(this)">
<a href="#">栏目1</a>
<!--栏目一 下拉菜单-->
<ul>
<li><a href="#">栏目1->菜单1</a></li>
<li><a href="#">栏目1->菜单2</a></li>
<li><a href="#">栏目1->菜单3</a></li>
<li><a href="#">栏目1->菜单4</a></li>
</ul>
</li>
<！--没加上js 鼠标事件-->
<li>
<a href="#">栏目2</a>
<!--栏目二 下拉菜单-->
<ul>
<li><a href="#">栏目1->菜单1</a></li>
<li><a href="#">栏目1->菜单2</a></li>
<li><a href="#">栏目1->菜单3</a></li>
<li><a href="#">栏目1->菜单4</a></li>
</ul>
</li>
<li><a href="#">栏目3</a> </li>
</ul>
</body>
</html>