I don't know why you have your own copy of calendar.js and iconGrid.js. Removing those modules would make this easier to review. In any case, you're extension seems to work fine, but to be extra sure, you should explicitly disconnect all signals to external objects you don't control (like Main.overview::hiding), all dbus signals (in CalendarServer) and all GObject signals that could still be emitted (such as GSettings)

Rejecting to get it off the queue.