Jquery、Ajax、xml实现三级联动菜单效果

<?xml version="1.0" encoding="utf-8"?>
<area Country="China">
 <province ID="1" provinceID="110000" province="北京市">
 <City CityID="110100" City="市辖区">
 <Piecearea PieceareaID="110101" Piecearea="东城区" />
 <Piecearea PieceareaID="110102" Piecearea="西城区" />
 <Piecearea PieceareaID="110103" Piecearea="崇文区" />
 <Piecearea PieceareaID="110104" Piecearea="宣武区" />
 <Piecearea PieceareaID="110105" Piecearea="朝阳区" />
 <Piecearea PieceareaID="110106" Piecearea="丰台区" />
 <Piecearea PieceareaID="110107" Piecearea="石景山区" />
 <Piecearea PieceareaID="110108" Piecearea="海淀区" />
 <Piecearea PieceareaID="110109" Piecearea="门头沟区" />
 <Piecearea PieceareaID="110111" Piecearea="房山区" />
 <Piecearea PieceareaID="110112" Piecearea="通州区" />
 <Piecearea PieceareaID="110113" Piecearea="顺义区" />
 <Piecearea PieceareaID="110114" Piecearea="昌平区" />
 <Piecearea PieceareaID="110115" Piecearea="大兴区" />
 <Piecearea PieceareaID="110116" Piecearea="怀柔区" />
 <Piecearea PieceareaID="110117" Piecearea="平谷区" />
 </City>
<province>

<h2>地区三级联动菜单</h2>
 省:<select id="province" onchange="showcity()"><option value="0">-请选择-</option></select>
 市:<select id="city" onchange="showdistrict()"><option value="0">-请选择-</option></select>
 地区:<select id="district"><option value="0">-请选择-</option></select>

//声明一个全局变量，用于存储第一次请求的xml信息,避免后续多次频繁请求xml
 var xmldom =null;
 //获取并显示省份信息
 function showprovince(){
 //使用ajax去服务器获得xml文件里面的省份信息
 $.ajax({
 url:'./ChinaArea.xml',
 //data:
 dataType:'xml',//相当于调用responseXML
 type:'get',
 success:function(msg){
 //将返回的xml信息赋予xmldom
 xmldom = msg;
 //获得province 元素节点对象
 var prov = $(msg).find('province');
 //遍历省份信息
 prov.each(function(k,v){
 var nm = $(this).attr('province');
 var id = $(this).attr('provinceID');
 //追加到指定的节点
 $('#province').append("<option value="+id+">"+nm+"</option>");
 });
 }

 });
 }
 //网页加载显示省份信息 
 $(function(){
 showprovince();
 });
 function showcity(){
 //获取 省份 的id
 var pid = $('#province option:selected').val();
 //根据xmldom信息 找到指定的省份节点
 var xml_province = $(xmldom).find('province[provinceID='+pid+']');
 // 获取对应所有县市节点
 var city = $(xml_province).find('City');
 //在遍历追加前，先清空此前已经显示的信息
 $('#city').empty();
 $('#city').append('<option value="0">-请选择-</option>');
 //遍历追加县市
 city.each(function(k,v){
 var nm = $(this).attr('City');
 var id = $(this).attr('CityID');
 $('#city').append('<option value='+id+'>'+nm+'</option>');
 });
 }
 //以下函数的逻辑与showcity()的逻辑一致
 function showdistrict(){
 //获取 县市 的id
 var cid = $('#city option:selected').val();
 //根据xmldom信息 找到指定的县市节点
 var xml_city = $(xmldom).find('City[CityID='+cid+']');
 // 获取对应所有地区节点
 var district = $(xml_city).find('Piecearea');
 $('#district').empty();
 $('#district').append('<option value="0">-请选择-</option>');
 district.each(function(k,v){
 var nm = $(this).attr('Piecearea');
 var id = $(this).attr('PieceareaID');
 $('#district').append('<option value='+id+'>'+nm+'</option>');
 });
 }