// The client event 'ActivationChanging' takes two parameters sender and e
// sender is the object which is raising the event
// e is the DropDownActivationEventArgs
function WebDropDown_ActivationChanging(sender, e) {
//Gets the new active DropDownItem object
var newActiveItem = e.getNewActiveItem();
//Gets the text of the new active item
var newItemText = newActiveItem.get_text();
if (!confirm("Are you sure you want to activate the item '" + newItemText + "'?"))
//Cancels the ActivationChanging event
e.set_cancel(true);
}