CODEWITHSUNDEEP
javascriptrxjsreactive-programming
Rogerio Chaves
Rogerio Chaves

Reputation: 2769

RxJS retry only last item, blocking the stream

I'm trying to use RxJS to process a stream of items, and I would like for it to retry any failures, preferentially with a delay (and exponential backoff if possible), but I need to guarantee the ordering so I effectively want to block the stream, and I don't want to reprocess any items that were already processed

So I was trying to play with retryWhen, following this example:

const { interval, timer } = Rx;
const { take, map, retryWhen, delayWhen, tap } = RxOperators;

const source = take(5)(interval(1000));

source.pipe(
  map(val => {
    if (val >= 3) {
      throw val;
    }
    return val;
  }),
  retryWhen(errors =>
    errors.pipe(
      delayWhen(val => timer(1000))
    )
  )
);

But the stream restarts at the beginning, it doesn't just retry the last one:

rxjs stream flowing

Is it possible to achieve what I want? I tried other operators from docs as well, no luck. Would it be kinda against RxJS philosophy somehow?

Upvotes: 0

Views: 450

Answers (1)

Amer
Amer

Reputation: 6706

The retryWhen should be moved to an inner Observable to handle the failed values only and keep the main Observable working.

Try something like the following:

// import { timer, interval, of } from 'rxjs';
// import { concatMap, delayWhen, map, retryWhen, take } from 'rxjs/operators';

const source = interval(1000).pipe(take(5));

source.pipe(
  concatMap((value) =>
    of(value).pipe(
      map((val) => {
        if (val >= 3) {
          throw val;
        }
        return val;
      }),
      retryWhen((errors) => errors.pipe(delayWhen(() => timer(1000))))
    )
  )
);

Upvotes: 1

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