Select ReplaySubject values emitted untill now

Question

Is there reliable solution to get a snapshot of values currently buffered in ReplaySubject?

I came up with something like this, but not sure how reliable this solution is:

replaySubject.pipe(
    takeUntil(timer(10).pipe(take(1)))
)

The timer factor above seems wrong to me as I have no warranty if all values have been emitted properly within given time (this applies to replay subjects with a lot of values).

AFAIK, the `ReplaySubject` emits all the buffered values at once, in an array. Wouldn't `subj.pipe(take(1))` be enough? — Andrei Gătej, Feb 17 '21 at 11:51
Nope, it would just re-emit the first value from the buffer - you can check out this https://stackblitz.com/edit/rxjs-bidpjt — gxx, Feb 17 '21 at 15:25

score 0 · Accepted Answer · answered Feb 17 '21 at 15:32

I think this can be an approach:

replay
  .pipe(
    buffer(timer(0)),
    take(1)
  )
  .subscribe(a => {
    console.log(`This is one time value ${a}`);
  });

StackBlitz demo.

The ReplaySubject, when a new subscriber is registered, it will emit its values synchronously:

for (let i = 0; i < copy.length && !subscriber.closed; i += infiniteTimeWindow ? 1 : 2) {
      subscriber.next(copy[i] as T);
    }

for this reason, we're using buffer(timer(0)): by the time the buffer's notifier(timer(0)) emits, the values will have already been added in the buffer's array. So, it will be able to emit all the ReplaySubject's accumulated values.

Nicely spotted the synchronous emition of buffered values. Too bad there isn't some kind of length of buffer on replay subject also. Anyway. Thank you for your input! :) — gxx, Feb 17 '21 at 20:38

Select ReplaySubject values emitted untill now

1 Answers1