兼容IE, Chrome的ajax function

var gAjax = (function () {
    /*
        paramObj:{
            url: request url,
            method: GET or POST,
            encode: character,
            param: post param,
            isAsync: boolean,
            returnType: xml/text,
            onAjaxComplete: function
        }
    */
    var _send_ajax = function (paramObj) {
        var url, method, encode, httpRequest, param, isAsync, parser, returnType;
        var onAjaxComplete;
        url = paramObj.url;
        method = paramObj.method.toUpperCase();
        encode = paramObj.encode;
        if (method == 'GET')
            param = null;
        else if (method == 'POST')
            param = paramObj.param;
        isAsync = paramObj.isAsync;
        returnType = paramObj.returnType || "xml";
        onAjaxComplete = paramObj.onAjaxComplete;
        if (window.ActiveXObject) {//IE
            httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
        } else {//FireFox,Chrome,Safari
            httpRequest = new XMLHttpRequest();
        }
        httpRequest.onreadystatechange = function () {
            ) {
                ) {
                    if (returnType.toUpperCase() == "XML") {
                        if (window.ActiveXObject) {//IE
                            parser = new ActiveXObject("Microsoft.XMLDOM");
                            parser.async = false;
                            parser.load(httpRequest.responseXML);
                        } else if (document.implementation.createDocument) {
                            try {//FireFox
                                parser = document.implementation.createDocument("", "", null);
                                parser.async = false;
                                parser = (new DOMParser()).parseFromString(httpRequest.responseText, "text/xml");
                            } catch (e) {//Chrome,Safari
                                var xmlhttp = new window.XMLHttpRequest();
                                xmlhttp.open("GET", httpRequest.responseText, false);
                                xmlhttp.send(null);
                                parser = xmlhttp.responseXML.documentElement;
                            }
                        }
                    } else {
                        parser = httpRequest.responseText;
                    }
                    onAjaxComplete.apply(_send_ajax, [parser]);
                } else {
                    alert("远程服务调用失败！");
                }
            }
        }
        httpRequest.open(method, url, isAsync);
        if (typeof encode != 'undefined')
            if (method == 'GET')
                httpRequest.setRequestHeader("Content-Type", "text/html;charset=" + encode);
            else if (method == 'POST')
                httpRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=" + encode);
        httpRequest.send(param);
    }
    return {
        sendAjax: _send_ajax
    }
})();