代码如下:
 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 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
 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
 if(window.addEventListener){ 
 h3s[0].addEventListener("click",function(){instance.toggledisplay(this);},false); 
 }else{ 
 h3s[0].onclick = function(){instance.toggledisplay(this);} 
 } 
 } 
 }
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