I understand the difference between Client-side and Server-side scripting. I have a javascript function and variable in my MasterPage:

<script language="JavaScript" type="text/javascript">
    var needToConfirm = false;
          window.onbeforeunload = confirmExit;
          function confirmExit()
          {
            if (needToConfirm)
            {
              needToConfirm = false;
              return "Currently in edit mode. If you leave the page now then you will lose unsaved changes."
            }
          }
</script>

Given the fact that on my ASP.NET (Client-side) I can change the value of my needToConfirm variable to true onClientClick but by default it is false. Here's an example.

 <asp:Button ID="btnEdit" runat="server" Text="  Edit  " onclick="btnEdit_Click" OnClientClick="needToConfirm = true;" />

Now the question here is when on the C# (Server-side) I have to set the needToConfirm to true under an if-statement but not necessarily on Page_Load:

private void SetDefault()

    if (Session[def.ID_CUST] != null)
    {
          //I want to change the variable value here
    }
}

Thanks.

UPDATE

I'm using .NET 2.0 Classic and WebForms

c# javascript asp.net
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