What's the motivation for ending a stream?

[LAC-Tech]

Hi, long time user, first time writer.

Reading the docs again, I notice that there's a concept of ending a stream. What's the motivation for that? I can't think of a scenario, but I'm sure you had one in mind.

[nordfjord]

Imagine you've got a timer and want to cancel it when listeners stop:

function interval(ms: number) {
  const s = stream()
  let i = 0;
  const interval = setInterval(()=> s(i++), ms)
  s.end.map(()=> clearInterval(interval))
  return s
}

interval(1000)
  .pipe(take(4))
// 1-2-3-4

This can be extrapolated for arbitrary cleanup logic for e.g. web sockets

[dehmer]

I assume take in the case must be aware of the additional protocol and has to actively close upstream interval when it's done. take probably also has to close itself so that an appropriate side-effect can be triggered. I this correct?

[nordfjord]

That sounds about right. Some of the built-in modules propagate ending downwards using a pattern like

const takeUntil = (term, src) =>
  flyd.endsOn(
    flyd.merge(term, src.end),
    flyd.combine((src, self) => {
      self(src());
    }, [src])
  );