public partial class _Default : System.Web.UI.Page 

{

    protected void Page_Load(object sender, EventArgs e)

    {

      

    }

    [WebMethod]

    public static string GetAvailableTickets()

    {

        int NoOfTicketsAvailable = 5;

        return NoOfTicketsAvailable.ToString();

    }

}

<script src="_scripts/jquery-1.2.6.js" type="text/javascript"></script>

        <script language="javascript">

            $(document).ready(function() {

                $("#txtNoOfTickets").blur(function() {

                    var ticketRequired = this.value;

                    var options = {

                        type: "POST",

                        url: "Default.aspx/GetAvailableTickets",

                        data: "{}",

                        contentType: "application/json; charset=utf-8",

                        dataType: "json",

                        success: function(response) {

var avilabletic = parseInt(response.d);                            

                            if (ticketRequired > avilabletic) {

                                alert("Only " + response.d + " tickets available!");

                            }

                            else {

                                alert(response.d);

                            }

 

                        }

                    };

                    //Call the PageMethods

                    $.ajax(options);

 

                });

            });

        </script>

 

<form id="form1" runat="server"> 

        <asp:TextBox ID="txtNoOfTickets" runat="server"></asp:TextBox>

</form>