ReferencemergeMap
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mergeMap
mergeMap
Runs inner streams in parallel.
Signature
mergeMap(project, concurrent?: number): OperatorFunctionMarble diagram
outer: --a---b---|
inner(a): --1-2-3|
inner(b): --1-2-3|
result: --1-2-1-3-2-3-|What it does
For each value it starts a new inner Observable, cancelling nothing. All active inner streams run in parallel (no limit by default). The concurrent parameter caps the number of simultaneous subscriptions — extras wait in a queue.
When to use
Parallel HTTP requests (loading a list of thumbnails, for example), handling events where order and cancellation don't matter. mergeMap(fn, 3) is the standard download-pool pattern.
Gotcha
Without concurrent, a stream of clicks gives you as many simultaneous requests as clicks. For critical operations, exhaustMap is preferable.
See also
switchMap, concatMap, forkJoin
script.ts
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