protected void Page_Load(object sender, EventArgs e)
        {
            Response.Clear();
            Response.ContentType = "text/xml";//设置输出的格式为XML
            Response.Charset = "UTF-8";//设置输出的编码为UTF-8
            this.GetXmlData();
        }
        private void GetXmlData()
        {

            StringBuilder xmlData = new StringBuilder();
            xmlData.AppendLine(@"<?xml version='1.0' encoding='UTF-8' ?>");
            xmlData.AppendLine(@"<response>");
            xmlData.AppendLine(@"<res>1111</res>");
            xmlData.AppendLine(@"</response>");
            Response.Write(xmlData.ToString());
        }

if (window.XMLHttpRequest) { //Mozilla 浏览器
            XMLHttpReq = new XMLHttpRequest();
        }
        else if (window.ActiveXObject) { // IE浏览器
            try {
                XMLHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    XMLHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) { }
            }
        }
        
        var url = "WebForm5.aspx";
        XMLHttpReq.open("GET", url, true);
        XMLHttpReq.onreadystatechange = function () {
            if (XMLHttpReq.readyState == 4) { // 判断对象状态
                if (XMLHttpReq.status == 200) { // 信息已经成功返回，开始处理信息
                    alert(XMLHttpReq.responseXML.getElementsByTagName("res").length);
                } else { //页面不正常
                    window.alert("您所请求的页面有异常。");
                }
            }
        }; //指定响应函数
        XMLHttpReq.send(null); // 发送请求

        protected void Page_Load(object sender, EventArgs e)
        {
            Response.Clear();
            Response.ContentType = "text/xml";//设置输出的格式为XML
            Response.Charset = "UTF-8";//设置输出的编码为UTF-8
            this.GetXmlData();
            Response.End();//////////
        }