Created
December 14, 2019 22:00
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Subscribe to multiple inner observables concurrently and emit results in order
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| import { | |
| from, | |
| BehaviorSubject, | |
| Observable, | |
| ObservableInput, | |
| ObservedValueOf, | |
| OperatorFunction, | |
| MonoTypeOperatorFunction, | |
| } from 'rxjs'; | |
| import { mergeMap, delayWhen, finalize, skipWhile, take } from 'rxjs/operators'; | |
| const delayUntilIsActiveIndex = <O extends ObservableInput<any>>( | |
| activeIndex$: Observable<number>, | |
| innerIndex: number | |
| ): MonoTypeOperatorFunction<O> => | |
| delayWhen(() => | |
| activeIndex$.pipe( | |
| skipWhile(activeIdx => activeIdx !== innerIndex), | |
| take(1) | |
| ) | |
| ); | |
| const bumpIndexOnComplete = <O extends ObservableInput<any>>( | |
| activeIndex$: BehaviorSubject<number>, | |
| innerIndex: number | |
| ): MonoTypeOperatorFunction<O> => finalize(() => activeIndex$.next(innerIndex + 1)); | |
| export function orderedMergeMap<T, O extends ObservableInput<any>>( | |
| project: (value: T, index: number) => O, | |
| concurrent = 5 | |
| ): OperatorFunction<T, ObservedValueOf<O>> { | |
| const activeIndex$ = new BehaviorSubject(0); | |
| return mergeMap( | |
| (value: T, index: number) => | |
| from(project(value, index)).pipe( | |
| delayUntilIsActiveIndex(activeIndex$, index), | |
| bumpIndexOnComplete(activeIndex$, index) | |
| ), | |
| concurrent | |
| ); | |
| } |
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