Call a ASP.NET method from Javascript

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ASP.NET

Javascript

Hi! I have a site and i want to set the user status in my database to 0 (Offline) when the user want to exit the site , the problem is i tried Page_Unload method but doesn't work and i found some Javascript code which works but this Javascript code shows a notification when you want to leave the site and in this code i want to call an ASP.NET method to change data in database but doesn't work.Thanks in advance!

// Javascript code
  window.onbeforeunload = confirmExit;

function confirmExit() {  
    PageMethods.OnlineOut();
}

//This is on my Master Page
 <script type="text/javascript" src='<%= ResolveClientUrl("~/JavaScript.js") %>'></script>

 <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
</asp:ScriptManager>

//This is on my Content Page.cs
 [WebMethod]
    public  void OnlineOut()
    {
        SqlConnection conexiune = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
                SqlCommand SetareOnline = new SqlCommand("Update [dbo].[Table] Set Online=0 Where(UserName=@UserName)", conexiune);
                SetareOnline.Parameters.AddWithValue("@UserName", Session["Login"].ToString());
                conexiune.Open();
                SetareOnline.ExecuteNonQuery();
                conexiune.Close();
    }