Confirmation message in Javascript

    function confirmDelete()
        {
       var IsOk = confirm('Are you sure you want to delete data?')
       if (IsOk)
          {
                return true;
          }
           else
            {
                return false;
             }
           }

Now call this javascript function on aspx page

<asp:Button ID="btnDelete" runat="server" Text="Delete" OnClick="btnDelete_Click"
 OnClientClick="return confirmDelete();" BackColor="#C0C0FF" BorderStyle="Ridge"
BorderWidth="1px" />