Ajax实现简单用户名重名查询

很早就想发布这篇POST了，Ajax实现简单用户名重名查询，引用了xmlhttprequest object pool，如下：

/**
* XMLHttpRequest Object Pool
*
* @author legend <legendsky@hotmail.com>
* @link http://www.ugia.cn/?p=85
* @Copyright www.ugia.cn
*/

var XMLHttp = {
_objPool: [],

    _getInstance: function ()
    {
        for (var i = 0; i < this._objPool.length; i ++)
        {
            if (this._objPool[i].readyState == 0 || this._objPool[i].readyState == 4)
            {
                return this._objPool[i];
            }
        }

// IE5中不支持push方法
this._objPool[this._objPool.length] = this._createObj();

return this._objPool[this._objPool.length - 1];
},

    _createObj: function ()
    {
        if (window.XMLHttpRequest)
        {
            var objXMLHttp = new XMLHttpRequest();

        }
        else
        {
            var MSXML = ['MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP'];
            for(var n = 0; n < MSXML.length; n ++)
            {
                try
                {
                    var objXMLHttp = new ActiveXObject(MSXML[n]);
                    break;
                }
                catch(e)
                {
                }
            }
         }

        // mozilla某些版本没有readyState属性
        if (objXMLHttp.readyState == null)
        {
            objXMLHttp.readyState = 0;

            objXMLHttp.addEventListener("load", function ()
                {
                    objXMLHttp.readyState = 4;

                    if (typeof objXMLHttp.onreadystatechange == "function")
                    {
                        objXMLHttp.onreadystatechange();
                    }
                }, false);
        }

return objXMLHttp;
},

    // 发送请求(方法[post,get], 地址, 数据, 回调函数)
    sendReq: function (method, url, data, callback)
    {
        var objXMLHttp = this._getInstance();

        with(objXMLHttp)
        {
            try
            {
                // 加随机数防止缓存
                if (url.indexOf("?") > 0)
                {
                    url += "&randnum=" + Math.random();
                }
                else
                {
                    url += "?randnum=" + Math.random();
                }

open(method, url, true);

                // 设定请求编码方式
                setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
                send(data);
                onreadystatechange = function ()
                {
                    if (objXMLHttp.readyState == 4 && (objXMLHttp.status == 200 || objXMLHttp.status == 304))
                    {
                        callback(objXMLHttp);

补充：Web开发 , 其他 ,