CODEWITHSUNDEEP
rxjs
user10103655
user10103655

Reputation: 131

Execute array of observables in sequence based on condition

Given an array of observables where each observable can emit EMPTY, how can I execute the next observable in the array on the condition that the previous observable returned EMPTY or stop iterating the array and return a non EMPTY value once an observable in the array has emitted the first non EMPTY value?

Upvotes: 1

Views: 267

Answers (1)

Andrei Gătej
Andrei Gătej

Reputation: 11924

Here would be one approach:

const emptyVal = Symbol('empty');

const src$ = concat(
    ...arrOfObservable.map(
      obs$ => obs$.pipe(
        last(null, emptyVal)
      )
    )
  ).pipe(
    filter(v => v !== emptyVal),
    first()
  )

The last() operator will emit the last emitted value, after the source completes. If there is no last value(obs$ has used EMPTY), it will emit emptyVal.

filter(v => v !== emptyVal) will make sure that we keep iterating until we get a non empty value.

With first(), we'd stop the iteration and we'd get the emitted value.

Note: this approach works if the obs$ completes at some time, otherwise last won't be able to do its job.

Upvotes: 1

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