In fact thinking of it as a set frees computing to do things concurrently invisibly. A lot of other comments here say "ah, but that's just JS iteration still".

In fact thinking of it as a set frees computing to do things concurrently invisibly. A lot of other comments here say "ah, but that's just JS iteration still"... but there's really nothing to prevent it being the equivalent of a Go routine... no order implied, no iteration implied, but all the things in the set will have the functions hide() or show() called.