StartEditing プロパティ

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

function WebTab1_StartEditing(sender, e) {
    var tab = sender;
    
    //Gets the index of the tab raising the event
    var tabIndex = e.get_tabIndex();

              
    //Assuming you have a label called labelOutput on the form
    var label = $get('labelOutput');

    if (tabIndex == 3) {
        //Cancels the StartEditing event
        e.set_cancel(true);

        label.innerHTML = "Editing not allowed for tab with index " + tabIndex +"!";
    }
    else
      
       label.innerHTML = "Editing started...";

   
}