unable to call webemothod present in asmx file using javascript

HI,
im trying to call webmethod:
what im coding is here:
my .aspx page:
 <asp:ScriptManager ID="MasterScriptManager" runat="server" EnablePageMethods="true">
        <Scripts>
        <asp:ScriptReference Path="~/Scripts/indexFunctions.js" />
        </Scripts>
        <Services>
        <asp:ServiceReference Path="Demo.asmx" />
        </Services>       
                </asp:ScriptManager>
 
.asmx file:
<%@ WebService Language="VB" CodeBehind="~/App_Code/Demo.vb" ...