I have a similar pattern when using an rxjs pipeline to do async tasks in response to changes in other values. The typical pattern would be readonly foo =

I have a similar pattern when using an rxjs pipeline to do async tasks in response to changes in other values. The typical pattern would be readonly foo = bar.pipe( switchMap(v => doTask(v)), shareReplay(1), ); Where doTask returns a promise or an AsyncSubject. The shareRelpay allows foo to cache the last value so any late subscriber will get the most recent value. This has a problem of returning cached values while new work is happening (eg while a network request is in progress) so instead I like to write readonly foo = bar.pipe( map(v => doTask(v), shareReplay(1), switchMap(v => v), ); This way the shareReplay is caching the promise instead of the result. With this pattern I can interact with this pipeline from code like so async someEventHandler(userInput) { this.bar.next(userInput); const result = await firstValueFrom(this.foo); … } Without the pattern, this code would get the old result if there was ever any cached value