ajax 实现城市，区域，道路 下拉列表级联。。主要还是js

<script type="text/javascript">
?? var xmlHttp;
?? function createXMLHttp(){
??? if(window.XMLHttpRequest){
???? xmlHttp=new XMLHttpRequest();
??? }
???? else if(window.ActiveXObject)
?? ?{
??? try{
????? //Firefox, Opera 8.0+, Safari
????? xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
??? }catch(e){
????? //Internet Explorer
????? try{
???? ??xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
???? }catch(e){
????? ?xmlHttp = false;
???? }
???? }
??}
???
?? }
??
?? function refreshArea(){
?? ?var cityid=document.getElementById("cityid").value;
?? ?createXMLHttp();
?? ?xmlHttp.onreadystatechange = refreshAreaCallback;
?? ?var urls="/area/area!findAreaByID.action?formInfo.FCITYID="+cityid;
?? ?xmlHttp.open("post",urls);
??xmlHttp.send(null);
?? }
??
??? function refreshAreaCallback(){
???? if(xmlHttp.readyState==4){
???? ?if(xmlHttp.status ==200){
???? ??var membersData = xmlHttp.responseXML.getElementsByTagName('name');
? ???var fid=xmlHttp.responseXML.getElementsByTagName('fid');
? ???var area=document.getElementById("areaid");
?????area.innerHTML='';
? ???area.options.add(new?? Option("--请选择","0"));?
? ???for(var i=0;i<membersData.length;i++){
? ????var areaname=membersData[i].firstChild.nodeValue;
? ????var areaid = fid[i].firstChild.nodeValue;
? ????area.options.add(new?? Option(areaname,areaid));??

?

?//js老是提示错误。找了很久，发现这个方法挺好。不知道还有没有更简单的方法
??????}
???? ?}
???? }
??? }
??
?? function refreshRoad(){
?? ? ?var FAREAID=document.getElementById("areaid").value;
?? ??createXMLHttp();
???? xmlHttp.onreadystatechange = refreshRoadCallback;
???? var url="/road/road!findRoadByID.action?formInfo.FAREAID="+FAREAID;
???? xmlHttp.open("post",url);
???? xmlHttp.send(null);
????
??? }
???
?? function refreshRoadCallback(){
???? if(xmlHttp.readyState==4){
???? ?if(xmlHttp.status ==200){
???? ??var membersData = xmlHttp.responseXML.getElementsByTagName('name');
? ???var fid=xmlHttp.responseXML.getElementsByTagName('fid');
? ???var road=document.getElementById("roadid");
? ???road.innerHTML='';
? ???road.options.add(new?? Option("--请选择","0"));?
? ???for(var i=0;i<membersData.length;i++){
? ????var deptname=membersData[i].firstChild.nodeValue;
? ????var deptid = fid[i].firstChild.nodeValue;
? ????road.options.add(new?? Option(deptname,deptid));
? ????}
???? ?}
???? }
??? }
?? </script>