<script type="text/javascript">
var level1 = ["Beijing", "GuangZhou", "ShangHai"];
var level2 = [["ZhaoYang", "TianTan", "GuGong"], ["Tianhe", "Panyu"], ["PuDong", "PuXi"]];
var level3 = [[["TianShan", "HuangShan"], ["TianTan1", "TianTan2"], ["GuGong1", "GuGong2", "GuGong3", "GuGong4"]], [["TianHe1", "TianHe2"], ["PanYu1", "PanYu2"]], [["PuDong1", "PuDong2"], ["PuXi1", "PuXi2"]]];
var Levels = {
fL: null,//用存储各级select的DOM引用
sL: null,
tL: null,
l1: null,
l2: null,
l3: null,
$: function(id){
return (typeof id == "object") ? id : document.getElementById(id);
},
init: function(fID, sID, tID, l1, l2, l3){
this.fL = this.$(fID);
this.sL = this.$(sID);
this.tL = this.$(tID);
this.l1 = l1;
this.l2 = l2;
this.l3 = l3;
this.fL.options.add(new Option("Select",-1));//给一级菜单添加一个“select”标志
for (var i = 0; i < l1.length; i++) {
var item = new Option(l1[i], i);
this.fL.options.add(item);
}
this.doLev2(); //调用doLev2函数，处理二级菜单
this.doLev3(); //调用doLev3函数，处理三级菜单
},
removeSTL: function(){ //用于删除第二、三级的菜单项
this.sL.options.length = 0;
this.tL.options.length = 0;
},
removeTL: function(){ //用于删除第三级的菜单项
this.tL.options.length = 0;
},
doLev2: function(){ //处理二级菜单
var that = this;
this.fL.onchange = function(){
that.removeSTL(); //删除旧second的select
if (that.fL.selectedIndex == 0) {
that.removeSTL(); // //删除旧second的select
}
else {
that.sL.options.add(new Option("Select", -1)); //给二级菜单添加一个“select”标志
//获取第二级所需的数组
var items = that.l2[that.fL.selectedIndex - 1];
for (var i = 0; i < items.length; i++) { //添加第二级的新select项
var item = new Option(items[i], i);
that.sL.options.add(item);
}
}
}
},
doLev3: function(){ //处理三级菜单
var that = this;
this.sL.onchange = function(){
that.removeTL(); //删除旧third的select
if (that.sL.selectedIndex == 0) {
that.removeTL(); //删除旧third的select
}
else {
that.tL.options.add(new Option("Select", -1)); //给三级菜单添加一个“select”标志
//获取第三级所需的数组
var items = that.l3[that.fL.selectedIndex - 1][that.sL.selectedIndex - 1];
for (var i = 0; i < items.length; i++) { //添加第三级的新select项
var item = new Option(items[i], i);
that.tL.options.add(item);
}
}
}
}
}
onload = function(){
Levels.init("first", "second", "third", level1,level2,level3); //调用Levels的init方法
}
</script>

<form>
<select id="first">
</select>
<select id="second">
</select>
<select id="third">
</select>
</form>