JQuery調webservice實現郵箱驗證（是否已被佔用）

 <asp:ScriptManager ID="ScriptManager1" runat="server">
    <Services>
    <asp:ServiceReference Path="~/WebService1.asmx" />
    </Services>
    </asp:ScriptManager> 

SinaWeiBo.WebService1.cunzai($(this).val(), a, b)
                        {
                            function a(result) {
                                if (result == "該郵箱已存在請重新輸入") {
                                    $('#txtusername').val('');
                                    $('#txtusername').focus();
                                    $('#emailyz').text(result);
                                }
                                else { $('#emailyz').text('可以使用'); }
                            }
                            function b() {
                                $('#emailyz').text('沒有傳回值');
                            }
                        }

webservice：

  public string cunzai(string txtusername)
        {
            //判斷郵箱存不存在
           

            try
            {
                SinaWeiBo.BLL.T_Users bt1 = new BLL.T_Users();
                DataSet ds = new DataSet();
                ds = bt1.GetList(" T_UserEmail='" + txtusername + "'");
                string cha = ds.Tables[0].Rows[0][0].ToString();
                return "該郵箱已存在請重新輸入";
            }
            catch {
                    return "正確";
            }
           
           
        }