本例是应用别人的例子，原来那位老兄是用一般方法写成的无限级折叠菜单，在此先感谢他！后来我就通过了一些简化修改，将原来的例子改成了面向对象的方式，实例中的展开与闭合的小图标可以自己重新添加，从而更好的查看效果。
<!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>很实用的JS+CSS多级树形展开菜单</title>
<style type="text/css">
body{margin:0;padding:0;font:12px/1.5 Tahoma,Helvetica,Arial,sans-serif;}
ul,li,{margin:0;padding:0;}
ul{list-style:none;}
a{text-decoration: none;}
#root{margin:10px;width:200px;overflow:hidden;}
#root li{line-height:25px;}
#root .rem{padding-left:16px;}
#root .add{background:url(treeico.gif) -4px -31px no-repeat;}
#root .ren{background:url(treeico.gif) -4px -7px no-repeat;}
#root li a{color:#666666;padding-left:5px;outline:none;blr:expression(this.onFocus=this.blur());}
#root .two{padding-left:20px;display:none;}
</style>
</head>
<body>
<ul id="root">
<li>
<label><a href="javascript:;">校讯通</a></label>
<ul class="two">
<li>
<label><a href="javascript:;">沈阳市</a></label>
<ul class="two">
<li>
<label><a href="javascript:;">二小</a></label>
<ul class="two">
<li><label><a href="javascript:;">二年级</a></label></li>
<li>
<label><a href="javascript:;">三年级</a></label>
<ul class="two">
<li>
<label><a href="javascript:;">一班</a></label>
<ul class="two">
<li><label><a href="javascript:;">张三</a></label></li>
<li>
<label><a href="javascript:;">王五</a></label>
<ul class="two">
<li><label><a href="javascript:;">班长</a></label></li>
<li><label><a href="javascript:;">学习委员</a></label></li>
</ul>
</li>
</ul>
</li>
<li><label><a href="javascript:;">实验班</a></label></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li>
<label><a href="javascript:;">抚顺市</a></label>
<ul class="two">
<li><label><a href="javascript:;">二小</a></label></li>
<li><label><a href="javascript:;">一中</a></label></li>
</ul>
</li>
</ul>
</li>
</ul>
<script type="text/javascript" >
/**一般JS方法
function addEvent(el,name,fn){//绑定事件
if(el.addEventListener) return el.addEventListener(name,fn,false);
return el.attachEvent('on'+name,fn);
}
function nextnode(node){//寻找下一个兄弟并剔除空的文本节点
if(!node)return ;
if(node.nodeType == 1)
return node;
if(node.nextSibling)
return nextnode(node.nextSibling);
}
function prevnode(node){//寻找上一个兄弟并剔除空的文本节点
if(!node)return ;
if(node.nodeType == 1)
return node;
if(node.previousSibling)
return prevnode(node.previousSibling);
}
addEvent(document.getElementById('root'),'click',function(e){//绑定点击事件，使用root根元素代理
e = e||window.event;
var target = e.target||e.srcElement;
var tp = nextnode(target.parentNode.nextSibling);
switch(target.nodeName){
case 'A'://点击A标签展开和收缩树形目录，并改变其样式
if(tp&&tp.nodeName == 'UL'){
if(tp.style.display != 'block' ){
tp.style.display = 'block';
prevnode(target.parentNode.previousSibling).className = 'ren'
}else{
tp.style.display = 'none';
prevnode(target.parentNode.previousSibling).className = 'add'
}
}
break;
case 'SPAN'://点击图标只展开或者收缩
var ap = nextnode(nextnode(target.nextSibling).nextSibling);
if(ap.style.display != 'block' ){
ap.style.display = 'block';
target.className = 'ren'
}else{
ap.style.display = 'none';
target.className = 'add'
}
break;
}
});
window.onload = function(){//页面加载时给有孩子结点的元素动态添加图标
var labels = document.getElementById('root').getElementsByTagName('label');
for(var i=0;i<labels.length;i++){
var span = document.createElement('span');
span.style.cssText ='display:inline-block;height:18px;vertical-align:middle;width:16px;cursor:pointer;';
span.innerHTML = ' '
span.className = 'add';
if(nextnode(labels[i].nextSibling)&&nextnode(labels[i].nextSibling).nodeName == 'UL')
labels[i].parentNode.insertBefore(span,labels[i]);
else
labels[i].className = 'rem'
}
}
**/
//面向对象方法
var Tree = function(o){
this.root = document.getElementById(o);
this.labels = this.root.getElementsByTagName('label');
var that = this;
this.int();
Tree.prototype.addEvent(this.root,'click',function(e){that.treeshow(e)});
}
Tree.prototype = {
int:function(){//初始化页面，加载时给有孩子结点的元素动态添加图标
for(var i=0;i<this.labels.length;i++){
var span = document.createElement('span');
span.style.cssText ='display:inline-block;height:18px;vertical-align:middle;width:16px;cursor:pointer;';
span.innerHTML = ' '
span.className = 'add';
if(this.nextnode(this.labels[i].nextSibling)&&this.nextnode(this.labels[i].nextSibling).nodeName == 'UL')
this.labels[i].parentNode.insertBefore(span,this.labels[i]);
else
this.labels[i].className = 'rem'
}
},
treeshow:function(e){
e = e||window.event;
var target = e.target||e.srcElement;
var tp = this.nextnode(target.parentNode.nextSibling);
switch(target.nodeName){
case 'A'://点击A标签展开和收缩树形目录，并改变其样式
if(tp&&tp.nodeName == 'UL'){
if(tp.style.display != 'block' ){
tp.style.display = 'block';
this.prevnode(target.parentNode.previousSibling).className = 'ren'
}else{
tp.style.display = 'none';
this.prevnode(target.parentNode.previousSibling).className = 'add'
}
}
break;
case 'SPAN'://点击图标只展开或者收缩
var ap = this.nextnode(this.nextnode(target.nextSibling).nextSibling);
if(ap.style.display != 'block' ){
ap.style.display = 'block';
target.className = 'ren'
}else{
ap.style.display = 'none';
target.className = 'add'
}
break;
}
},
addEvent:function(el,name,fn){//绑定事件
if(el.addEventListener) return el.addEventListener(name,fn,false);
return el.attachEvent('on'+name,fn);
},
nextnode:function(node){//寻找下一个兄弟并剔除空的文本节点
if(!node)return ;
if(node.nodeType == 1)
return node;
if(node.nextSibling)
return this.nextnode(node.nextSibling);
},
prevnode:function(node){//寻找上一个兄弟并剔除空的文本节点
if(!node)return ;
if(node.nodeType == 1)
return node;
if(node.previousSibling)
return prevnode(node.previousSibling);
}
}
tree = new Tree("root");//实例化应用
</script>
</body>
</html>