TabAdded プロパティ (TabClientEvents)

// The client event TabAdded takes two parameters sender and e
       // sender  is the object which is raising the event
       // e is the TabItemPostBackEventArgs

       function WebTab1_TabAdded(sender, e) {

                      //Gets the index where a new tab is going to be added
                      var tabIndex = e.get_tabIndex();

//Assuming you have a label called labelOutput on the form
            var label = $get('labelOutput');
                     
label.innerHTML = "New tab added at index '" + tabIndex + "'!";

                      

                  }