From my experience in programming small imperative scrips for personal usage with JavaScript,
I can conclude that an event is "A perceived change in the output of a system" (such as clicking a link from client side or refreshing a page from server side),
while a mode is a situation or "state of affairs" of a program (such as a "saved game" state we can later "load") and if a certain state has happened the program can behave in some way (such as terminating itself).
But if at all, are event and mode well defined terms in CS literature and if so, what is the difference between them?