// The client event TabMoved takes two parameters sender and e
// sender is the object which is raising the event
// e is the TabMovedEventArgs
function WebTab1_TabMoved(sender, e) {
//Gets the initial index of the tab
var tabIndex = e.get_tabIndex();
//Gets the index of the tab when it is moving
var tabVisibleIndex = e.get_tabVisibleIndex();
//Assuming you have a label called labelOutput on the form
var label = $get('labelOutput');
label.innerHTML = "Tab Index : " + tabIndex + " ; Tab Visible Index : " + tabVisibleIndex;
}