In rxjs, given any Observable we can do observable.pipe(finalize(() => some_cleanup()) to run some_cleanup in any case (error or completion).

I was wondering if there is the errrr…. opposite of it, like an initialize() to run some setup code upon subscription.

Like this:

new_observable = observable.pipe(
  initialize(() => setup_things()),
  finalize(() => some_cleanup()),
)

Later we can subscribe to new_observable conveniently without even wondering if we need to setup something beforehand.