代码优化。解决办法

文件名：next.js

var $ = function (id) {
    return "string" == typeof id ? document.getElementById(id) : id;
};

function addEventHandler(oTarget, sEventType, fnHandler) {
    if (oTarget.addEventListener) {
        oTarget.addEventListener(sEventType, fnHandler, false);
    } else if (oTarget.attachEvent) {
        oTarget.attachEvent("on" + sEventType, fnHandler);
    } else {
        oTarget["on" + sEventType] = fnHandler;
    }
};

function Each(arrList, fun){
    for (var i = 0, len = arrList.length; i < len; i++) { fun(arrList[i], i); }
};

function GetOption(val, txt) {
    var op = document.createElement("OPTION");
    op.value = val; op.innerHTML = txt;
    return op;
};

var Class = {
  create: function() {
    return function() {
      this.initialize.apply(this, arguments);
    }
  }
}

Object.extend = function(destination, source) {
    for (var property in source) {
        destination[property] = source[property];
    }
    return destination;
}


var CascadeSelect = Class.create();
CascadeSelect.prototype = {
  //select集合，菜单对象
  initialize: function(arrSelects, arrMenu, options) {
    if(arrSelects.length <= 0 || arrMenu.lenght <= 0) return;//菜单对象
    
    var oThis = this;
    
    this.Selects = [];//select集合
    this.Menu = arrMenu;//菜单对象
    
    this.SetOptions(options);
    
    this.Default = this.options.Default || [];
    
    this.ShowEmpty = !!this.options.ShowEmpty;
    this.EmptyText = this.options.EmptyText.toString();
    
    //设置Selects集合和change事件
    Each(arrSelects, function(o, i){
        addEventHandler((oThis.Selects[i] = $(o)), "change", function(){ oThis.Set(i); });
    });
    
    this.ReSet();
  },
  //设置默认属性
  SetOptions: function(options) {
    this.options = {//默认值
        Default:    [],//默认值(按顺序)
        ShowEmpty:    true,//是否显示空值(位于第一个)
        EmptyText:    "请选择"//空值显示文本(ShowEmpty为true时有效)
    };
    Object.extend(this.options, options || {});
  },
  //初始化select
  ReSet: function() {
  
    this.SetSelect(this.Selects[0], this.Menu, this.Default.shift());
    this.Set(0);
  },
  //全部select设置
  Set: function(index) {
    var menu = this.Menu
    
    //第一个select不需要处理所以从1开始
    for(var i=1, len = this.Selects.length; i < len; i++){
        if(menu.length > 0){
            //获取菜单
            var value = this.Selects[i-1].value;
            if(value!=""){
                Each(menu, function(o){ if(o.val == value){ menu = o.menu || []; } });
            } else { menu = []; }
            
            //设置菜单
            if(i > index){ this.SetSelect(this.Selects[i], menu, this.Default.shift()); }
        } else {
            //没有数据
            this.SetSelect(this.Selects[i], [], "");
        }
    }
    //清空默认值
    this.Default.length = 0;
  },
  //select设置
  SetSelect: function(oSel, menu, value) {
    oSel.options.length = 0; oSel.disabled = false;
    if(this.ShowEmpty){ oSel.appendChild(GetOption("", this.EmptyText)); }
    if(menu.length <= 0){ oSel.disabled = true; return; }
    
    Each(menu, function(o){
        var op = GetOption(o.val, o.txt ? o.txt : o.val); op.selected = (value == op.value);
        oSel.appendChild(op);
    });    
  }
};

window.onload=function(){
    
    var menu = [
        {'val': 'AAA', 'menu': [
            {'val': 'aaaaaaaa1'},
            {'val': 'aaaaaaaa2'},
            {'val': 'aaaaaaaa3'},
            {'val': 'aaaaaaaa4'},
            {'val': 'aaaaaaaa5'}
        ]},
        {'val': 'BBB', 'menu': [
            {'val': 'bbbbbbb1'},
            {'val': 'bbbbbbb2'},
            {'val': 'bbbbbbb3'},
            {'val': 'bbbbbbb4'},
            {'val': 'bbbbbbb5'}
        ]},
        {'val': 'CCC', 'menu': [
            {'val': 'ccccccc1'},
            {'val': 'ccccccc2'},
            {'val': 'ccccccc3'},
            {'val': 'ccccccc4'},
            {'val': 'ccccccc5'}
        ]}
    ];
    
    var sel=["main_menu", "next_menu"];
    
    var val=["主菜单", "子菜单"];
    
    var cs = new CascadeSelect(sel, menu, { Default: val });
}