JavaScript 双级下拉菜单实现代码

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> 
<title>JavaScript下拉菜单</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:40px; 
}/*可有可无属性，是内容与边的距离*/ 
#navigation li { 
float:left; 
text-align:center; 
position:relative;/*position:relative一定要写，是下面的链接相对它绝对定位*/ 
} 
#navigation li a:link, #navigation li a:visited { 
display:block; 
text-decoration:none; 
color:#000; 
width:120px;/*改变所有的导航栏的长度*/ 
height:30px;/*改变所有导航栏的高度*/ 
line-height:30px; 
border:1px solid red;/*没有这个属性的所有的导航栏的颜色就连在一起了*/ 
background:#c5dbf2; 
padding-left:10px; 
} 
#navigation li ul { 
display:none; 
position:absolut; 
top:40px; 
left:0; 
margin-top:1px;/*可有可无，无的话主菜单和二级菜单就会没有空隙*/ 
width:120px; 
} 
#h{ 
    position:absolute; 
    top:74px; 
    left: 40px; 
} 
</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"> 
<li onmouseover="displaySubMenu(li1)" onmouseout="hideSubMenu(this)" id="li1">栏目1 
        <ul> 
            <li>栏目2->菜单1</li> 
            <li>栏目1->菜单2</li> 
            <li>栏目1->菜单3</li> 
        </ul> 
</li> 
<li onmouseover="displaySubMenu(this)" onmouseout="hideSubMenu(this)">栏目1 
        <ul> 
            <li>栏目1->菜单1</li> 
            <li>栏目1->菜单2</li> 
        </ul> 
</li> 
<li onmouseover="displaySubMenu(this)" onmouseout="hideSubMenu(this)">栏目1 
        <ul> 
            <li>栏目1->菜单1</li> 
            <li>栏目1->菜单2</li> 
            <li>栏目1->菜单3</li> 
        </ul> 
</li> 
</ul> 
 
 
</body> 
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]