JS模拟的QQ面板上的多级可展开的菜单

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> 
<HTML> 
<HEAD> 
<TITLE>QQ菜单</TITLE> 
</HEAD> 
<BODY> 
<script> 
if (!document.getElementById) 
document.getElementById = function() { return null; } 
function initializeMenu(menuId, actuatorId) { 
var menu = document.getElementById(menuId); 
var actuator = document.getElementById(actuatorId); 
if (menu == null || actuator == null) return; 
actuator.parentNode.style.backgroundImage = "url(/images/plus.gif)"; 
actuator.onclick = function() { 
var display = menu.style.display; 
this.parentNode.style.backgroundImage = 
(display == "block") ? "url(/images/plus.gif)" : "url(/images/minus.gif)"; 
menu.style.display = (display == "block") ? "none" : "block"; 
return false; 
} 
} 
window.onload = function() { 
initializeMenu("productsMenu", "productsActuator"); 
initializeMenu("newPhonesMenu", "newPhonesActuator"); 
initializeMenu("compareMenu", "compareActuator"); 
} 
</script> 
<style> 
body { 
font-family: verdana, helvetica, arial, sans-serif; 
} 
#mainMenu { 
background-color: #EEE; 
border: 1px solid #CCC; 
color: #000; 
width: 203px; 
} 
#menuList { 
margin: 0px; 
padding: 10px 0px 10px 15px; 
} 
li.menubar { 
background: url() no-repeat 0em 0.3em; 
font-size: 12px; 
line-height: 1.5em; 
list-style: none outside; 
} 
.menu, .submenu { 
display: none; 
margin-left: 15px; 
padding: 0px; 
} 
.menu li, .submenu li { 
background: url() no-repeat 0em 0.3em; 
list-style: none outside; 
} 
a.actuator { 
background-color: transparent; 
color: #000; 
font-size: 12px; 
padding-left: 15px; 
text-decoration: none; 
} 
a.actuator:hover { 
text-decoration: underline; 
} 
.menu li a, .submenu li a { 
background-color: transparent; 
color: #000; 
font-size: 12px; 
padding-left: 15px; 
text-decoration: none; 
} 
.menu li a:hover, submenu li a:hover { 
text-decoration: underline; 
} 
span.key { 
text-decoration: underline; 
} 
</style> 
</head> 
<body> 
 
<ul id="menuList"> 
<li class="menubar"> 
我有朋友圈 
<ul id="productsMenu" class="menu"> 
<li> 
我的好友 
<ul id="newPhonesMenu" class="submenu"> 
<li>张三[10000001]</li> 
<li>李四[10000002]</li> 
<li>李四[10000002]</li> 
</ul> 
</li> 
<li> 
陌生人 
<ul id="compareMenu" class="submenu"> 
<li>张三[10000001]</li> 
<li>李四[10000002]</li> 
</ul> 
</li> 
</ul> 
</li> 
</ul> 
 
</body> 
</BODY> 
</HTML>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]