js类后台管理菜单类-MenuSwitch

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);} 
            } 
        } 
    }

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