写MenuSwitch类的出发点是因为随着后台管理项越来越多，从而导致菜单显示部出现了滚动条导致页面很不美观，自己蒙生写这个JS类了。
这个功能类采用了目前比较流行的Web2.0做法，使用DIV+CSS+JS方式，将样式和功能分开。我下面先把演示效果放出来吧
function MenuSwitch(className){
this._elements = [];
this._default = -1;
this._className = className;
this._previous = false;
}
MenuSwitch.prototype.setDefault = function(id){
this._default = Number(id);
}
MenuSwitch.prototype.setPrevious = function(flag){
this._previous = Boolean(flag);
}
MenuSwitch.prototype.collectElementbyClass = function(){
this._elements = [];
var allelements = document.getElementsByTagName("div");
for(var i=0;i<allelements.length;i++){
var mItem = allelements[i];
if (typeof mItem.className == "string" && mItem.className == this._className){
var h3s = mItem.getElementsByTagName("h3");
var uls = mItem.getElementsByTagName("ul");
if(h3s.length == 1 && uls.length == 1){
h3s[0].style.cursor = "hand";
if(this._default == this._elements.length){
uls[0].style.display = "block";
}else{
uls[0].style.display = "none";
}
this._elements[this._elements.length] = mItem;
}
}
}
}
MenuSwitch.prototype.open = function(mElement){
var uls = mElement.getElementsByTagName("ul");
uls[0].style.display = "block";
}
MenuSwitch.prototype.close = function(mElement){
var uls = mElement.getElementsByTagName("ul");
uls[0].style.display = "none";
}
MenuSwitch.prototype.isOpen = function(mElement){
var uls = mElement.getElementsByTagName("ul");
return uls[0].style.display == "block";
}
MenuSwitch.prototype.toggledisplay = function(header){
var mItem;
if(window.addEventListener){
mItem = header.parentNode;
}else{
mItem = header.parentElement;
}
if(this.isOpen(mItem)){
this.close(mItem);
}else{
this.open(mItem);
}
if(!this._previous){
for(var i=0;i<this._elements.length;i++){
if(this._elements[i] != mItem){
var uls = this._elements[i].getElementsByTagName("ul");
uls[0].style.display = "none";
}
}
}
}
MenuSwitch.prototype.init = function(){
var instance = this;
this.collectElementbyClass();
if(this._elements.length==0){
return;
}
for(var i=0;i<this._elements.length;i++){
var h3s = this._elements[i].getElementsByTagName("h3");
if(window.addEventListener){
h3s[0].addEventListener("click",function(){instance.toggledisplay(this);},false);
}else{
h3s[0].onclick = function(){instance.toggledisplay(this);}
}
}
}