To be even more memory conscious, don't instantiate "myDataCalendar" until you have to use it. Your suggestion indicates you're doing it whenever the object/class instantiates.
function ChangeWeekHandler(Event){ if(!myDataCalendar) myDataCalendar = new ArrayCollection(); . . . } On top of that, make sure you free it up (in the case garbage collection doesn't pick it up). You can do this by simply setting it to null when you're done with it. myDataCalendar = null;