Ajax获取前台的数据

 前台：

function yz2() {
       var username = $("#TextBox1").val();
       $.ajax({
           type: "POST",
           url: "UserAdd.aspx?action=ajax",
           data: "username=" + username,
           success: function (msg) {
               // alert(msg);
               $("#TextBox1").after("<div id='msg'>"+msg+"</div>");//在文本框后面显示

                if (msg.indexOf("用户名已经存在") > -1) {

                    //判断按钮是否可用
                    $("#Button1").attr("disabled", true);
                }
                else {
                    $("#Button1").attr("disabled", false);
                }
           }
       });
       $('#msg').remove();
       return true;
   }

 后台：
            if(!String.IsNullOrEmpty(Request ["action"])&& Request["action"]=="ajax")
            {
               
                string username = Request["username"];

                TextBox1.Attributes.Add("onblur", "return yz2()");