TabAdding プロパティ

// The client event TabAdding takes two parameters sender and e
// sender  is the object which is raising the event
// e is the TabItemCancelEventArgs

 function WebTab1_TabAdding(sender, e) {

        //Gets the index where a new tab is going to be added

           var tabIndex = e.get_tabIndex();

                      if (tabIndex>19)

                      //Cancels the TabAdding event if tab index greater than 19
                          e.set_cancel(true); 

                  }