AJAX的队列请求如何实现（附代码）

//Ajax Function
var reqObj; //Creat Null Instence
var RequestArray = new Array();
//var whichRequest;
//加入请求队列
function AddRequestArray(url,isAsy,method,parStr,callBackFun)
{
 var ArgItem = new Array();
 ArgItem[0]=url;
 ArgItem[1]=isAsy;
 ArgItem[2]=method;
 ArgItem[3]=parStr;
 ArgItem[4]=callBackFun;
 RequestArray.push(ArgItem); //将当前请求添加到队列末尾
 if(RequestArray.length==1) //如果请求队列里只有当前请求立即要求执行队列，如果有其他请求，那么就不要求执行队列
 {
 ExeRequestArray();
 }
}
//执行队列里的顺序第一个的请求
function ExeRequestArray()
{
 if( RequestArray.length>0) //如果队列里有请求执行 AJAX请求
 {
 var ArgItem = RequestArray[0]; DoRequest(ArgItem[0],ArgItem[1],ArgItem[2],ArgItem[3],ArgItem[4]);
 }
}
//Run Ajax (string urladdress,bool IsAsy,string method,string parameters,string whichRequest)
function DoRequest(url,isAsy,method,parStr,callBackFun) 
{
 reqObj = false;
 //whichRequest = whichReq;
 if (window.XMLHttpRequest) //compatible Mozilla, Safari,...
 {
 reqObj = new XMLHttpRequest(); //Creat XMLHttpRequest Instance
 if (reqObj.overrideMimeType) //if Mime Type is false ,then set MimeType 'text/xml'
 {
 reqObj.overrideMimeType('text/xml');
 }
 }
 else if (window.ActiveXObject) //compatible IE
 {
 try
 {
 reqObj = new ActiveXObject("Msxml2.XMLHTTP"); //Creat XMLHttpRequest Instance
 }
 catch (e)
 {
 try
 {
 reqObj = new ActiveXObject("Microsoft.XMLHTTP"); //Creat XMLHttpRequest Instance
 }
 catch (e)
 {}
 }
 }
 //if reqObj is false,then alert warnning
 if (!reqObj)
 {
 alert('Giving up :( Cannot create an XMLHTTP instance');
 return false;
 }
 reqObj.onreadystatechange = function(){GetRequest(callBackFun)}; //set onreadystatechange Function
 reqObj.open(method, url, isAsy); //set open Function
 reqObj.setRequestHeader('Content-Type','application/x-www-form-urlencoded'); //set RequestHeader
 reqObj.send(parStr); //do send and send parameters 
}
//get Service Response information Function
function GetRequest(callBackFun)
{
 //judge readystate information
 if (reqObj.readyState == 4)
 {
 //judge status information
 if (reqObj.status == 200)
 {
 eval(callBackFun+"(reqObj)");
 }
 else
 {
 alert('There was a problem with the request.'+reqObj.status+"CallFunction:"+callBackFun); //else alert warnning
 }
 RequestArray.shift(); //移除队列里的顺序第一个的请求，即当前已经执行完成的请求
 ExeRequestArray(); //要求执行队列中的请求
 }
}