AJAX无刷新登录有关问题

var xmlhttp;
        function creatHttp() {
            if (window.ActiveXObject) {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            else {
                xmlhttp = new XMLHttpRequest();
            }
        }

        function postData() {
            creatHttp();
            var uname = document.getElementById("Text1").value;
            var upass = document.getElementById("Text2").value;
            if (uname.length == 0 || upass.length == 0) {
                alert("请输入用户名密码！");
                return;
            }
            else {
                var userinfo = "";
                userinfo = uname + "," + upass;
                xmlhttp.open("post", "Index/DataPage.aspx?userinfo=" + escape(userinfo), true);
                xmlhttp.onreadystatechange = stateChange;
                xmlhttp.send(null);
            }
        }

        function stateChange() {
            if (xmlhttp.readystate == 4) {
                if (xmlhttp.status == 200) {
                    document.getElementById("login").innerHTML = unescape(xmlhttp.ResponseText);
                }
            }
            else {
                alert("用户名密码错误！");
            }
        }

protected void Page_Load(object sender, EventArgs e)
    {
        Users users = new Users();
        string userinfo = Request.QueryString["userinfo"];
        string[] arr = userinfo.Split(',');
        string uname = arr[0].ToString();
        string upass = arr[1].ToString();
        users.Uname = uname;
        users.Upass = upass;
        DataSet ds = users.CheckUser(users);
        if (ds.Tables[0].Rows.Count > 0)
        {
            Response.Write("欢迎" + uname + "登录!");
        }
    }