封装XMLHttpReuqest

//xmlHttp.js
var Request = new Object();
Request.reqList = [];
function createXMLRequest()
{
    var xmlHttp=false;
    try {
        xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
    catch (e){
      try {
          xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
      }
     catch (E){
          xmlHttp = false;
      }
    }
    if (!xmlHttp && typeof XMLHttpRequest!='undefined')
    {
        xmlHttp = new XMLHttpRequest();
    }
    return xmlHttp;
}

Request.send = function(url, method, callback, data)
{
    var xmlHttp=createXMLRequest();
    xmlHttp.onreadystatechange = function()
    {
    if (xmlHttp.readyState == 4)
    {
           if (xmlHttp.status < 400)
           {
                callback(xmlHttp,data);
           }
           else
           {
               alert("当加载数据时发生错误 :\n" + xmlHttp.status+ "/" + xmlHttp.statusText);
           }
           //删除XMLHTTP，释放资源
           try {
               delete xmlHttp;
               xmlHttp = null;
           } catch (e) {}
       }
   }
   //如果以POST方式回发服务器
   if (method=="POST")
   {
       xmlHttp.open("POST", url, true);
       xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
       xmlHttp.send(data);
       Request.reqList.push(xmlHttp);
   }
   //以GET方式请求
   else
   {
       xmlHttp.open("GET", url, true);
       xmlHttp.send(null);
       Request.reqList.push(xmlHttp);
   }
   return xmlHttp;
}
//全部清除XMLHTTP数组元素，释放资源
Request.clearReqList = function()
{
    var ln = Request.reqList.length;
    for(var i=0; i<ln; i++)
    {
        var xmlHttp = Request.reqList[i];
        if(xmlHttp)
        {
            try{
                delete xmlHttp;
            } catch (e) {}
        }
    }
    Request.reqList = [];
}

//进一步封装XMLHTTP以GET方式发送请求时的代码
Request.sendGET = function(url,callback)
{
    Request.clearReqList();
   return Request.send(url, "GET", callback, null);
}
//进一步封装XMLHTTP以POST方式发送请求时的代码
Request.sendPOST = function(url, callback,data)
{
    Request.clearReqList();
   Request.send(url, "POST", callback, data);
}

HelloWorld 示例:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>无标题页</title>
    <script type="text/javascript" src="xmlHttp.js"></script>
    <script type="text/javascript">
    function callback(req,data)
    {
        document.getElementById("msg").innerHTML = req.responseText;
    }
    </script>
</head>
<body>
    <input id="Button1" type="button" value="button" onclick="Request.sendGET('HelloWorld.txt', callback)" />
    <div id="msg"></div>
</body>
</html>

HelloWorld.txt
就一行:HelloWorld