// The client event AjaxLoaded takes two parameters sender and e
// sender is the object which is raising the event
// e is the TabItemEventArgs
function WebTab1_AjaxLoaded(sender, e) {
var tab = sender;
//Gets the index of the tab raising the client event
var tabIndex = e.get_tabIndex();
//Gets the collection of tabs
var tabs = tab.get_tabs();
//Gets the text of the tab raising the event
var tabText = tabs[tabIndex].get_text();
//Assuming you have a label called labelOutput on the form
var label = $get('labelOutput');
label.innerHTML = "Ajax loaded for tab with index " + tabIndex;
}