js 控制网页不刷新检测用户名的方法

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

public partial class VerifyUserName : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            string userName = Request.QueryString["userName"];
            VerifyMyUserName(userName);
        }
    }

    private void VerifyMyUserName(string userName)
    {
        bool result = false;
        SqlConnection conn = new SqlConnection();
        conn.ConnectionString = "Data Source=FIREWOOD-PC;Initial Catalog=member;User ID=sa;Password=自己改吧;Pooling=False";
        try
        {
            conn.Open();
            string sql = "select COUNT(*) from Member where [Name]='" + userName+"'";
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataReader rdr = cmd.ExecuteReader();
            if (rdr.Read())
            {
                result = rdr.GetInt32(0) > 0;
            }
            conn.Close();
            if (result)
            {
                WriteHtmlMsg("existed");
            }
            else
            {
                WriteHtmlMsg("failed");
            }
        }
        catch
        {
        }
        finally
        {
            conn.Close();
        }
    }

    /// <summary>
    /// 写Html到页面
    /// </summary>
    /// <param name="msg"></param>
    private void WriteHtmlMsg(string msg)
    {
        Response.ClearContent();
        Response.Cache.SetNoStore();
        Response.ContentType = " text/html";
        Response.ContentEncoding = System.Text.Encoding.UTF8;
        Response.Write(msg);
    }
}

 $(document).ready(function(){
        $("#txtUserName").blur(function(){
            var userName = $("#txtUserName").val();
             $.ajax({
                    async: false, // 此处要设置为同步
                    cache: true, // 默认true,设置为 false 将不会从浏览器缓存中加载请求信息。
                    type: "GET", // 默认:GET 请求方式:[POST/GET]
                    url: "VerifyUserName.aspx", // 默认当前地址,发送请求的地址
                    data: { userName: userName}, // 发送到服务器的数据
                    error: function(XMLHttpRequest, textStatus, errorThrown) { alert(XMLHttpRequest + "," + textStatus + "," + errorThrown); }, // 请求失败时调用
                    timeout: 6000, // 设置请求超时时间
                    success: function(msg) {
                        if (msg == "existed"){
                            //在页面上显示此用户名已经存在
                            $("#lblExistMsg").html("此用户名已经存在!")
                        }
                        else{
                            $("#lblExistMsg").html("此用户名不存在，可以注册!")
                        }
                    },
                    complete: function() {
                    }
                });
        });
    });