javascript 三级下拉选择菜单Levels对象

代码如下：

<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>

代码如下：

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