Jquery's Ajax Property For Asp.Net 2.0

$.ajax({
                    type: "POST",
                    contentType: "application/json; charset=utf-8",
                    url: "WebService.asmx/HelloWorld",
                    data: "{}",
                    dataType: "json",
                    success: function(msg) {
                        alert(msg.d);
                    }
                });

[System.Web.Script.Services.ScriptService]
public class Service : System.Web.Services.WebService

[ScriptMethod(ResponseFormat = ResponseFormat.Json)]

$(document).ready(function() {
        $('#clKaydet').click(function() {
            $.ajax({
                type: "POST",
                contentType: "application/json; charset=utf-8",
                url: "WebService.asmx/HelloWorld",
                data: "{}",
                dataType: "json",
                success: function(msg) {
                    alert(msg);
                }
            });

        });

    });

<form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" EnablePageMethods="true" runat="server" />
    <div>

        <input type="button" id="clKaydet" runat="server" value="Kayıt" onclick="Kayit()" />
    </div>

    </div>
    </form>

<WebMethod()> _
Public Function HelloWorld() As String
    Dim sText As String = "Hello"
    Return sText
End Function