var pool_xmlreq=function(){
var _cachecase=[];
 _cachecase.fetch=function(){
  var i=0;
  var _instance=function(){
   try{
    return (new activexobject(msxml2.xmlhttp.5.0));}
   catch(e){
    try{
     return (new xmlhttprequest());}
    catch(e){
     try{
      return (new activexobject(msxml2.xmlhttp));}
     catch(e){
      try{
       return (new activexobject(microsoft.xmlhttp));}
      catch(e){
       alert(error: initializing xmlhttprequest!);}}}}}
  for(;i   if(this[i].readystate==0||this[i].readystate==4){
    return this[i];}}
  this[i]=_instance();
  return this[i];}
 this.length=function(){
  return _cachecase.length}
 this.instance=function(){
  return _cachecase.fetch()}
 this.connect=function(method,url,data,handler){
  var _xmlhttpreq=_cachecase.fetch();
  with(_xmlhttpreq){
   open(method,url,true);
   setrequestheader(cache-control,no-cache);  
   setrequestheader(content-type,application/x-www-form-urlencoded;charset=utf-8);
   send(data);
   onreadystatechange=function(){
    if(_xmlhttpreq.readystate     return false;
    if(_xmlhttpreq.status==200||_xmlhttpreq.status==304){
     handler(decodeuricomponent(_xmlhttpreq.responsetext));
     return true;}
    alert(error: status_+_xmlhttpreq.status+!);
    return false;}}}
}
var xmlreq=new pool_xmlreq();
用法:
xmlreq.connect(post,url,postdata,function);