CODEWITHSUNDEEP
javascriptrxjsobservable
Raphaël Balet
Raphaël Balet

Reputation: 8491

How can I `await` on an Rx Observable to have a specific value?

I'd like to await an observable to have a define value before moving forward.

I tried the follwoing, but it is not working, even if myObservable$ is instantiated with a value

await lastValueFrom(this.myObservable$.pipe(filter((event) => (event == 'something' ? true : false))))

Context

In angular, while loading the app inside an iFrame, I need a token that may exists locally or being set by the parent.

If this is set by the parent, I would like my guard to await till the token has been value.

Workaround

I've create an observable only for this purpose, so I could use the await lastValueFrom(this.myObservable$) and this is working, but I'm just wondering if it was possible to await a specific value.

Upvotes: 0

Views: 733

Answers (2)

BizzyBob
BizzyBob

Reputation: 14740

In order for lastValueFrom to emit anything, its observable source must complete (otherwise, there is no "last" value).

You can force it to complete by using take(1) after your filter condiation:

await lastValueFrom(this.myObservable$.pipe(
    filter(event => event === 'something'),
    take(1)
));

Upvotes: 1

Oliver Weichhold
Oliver Weichhold

Reputation: 10296

Sure, use takeWhile.

await lastValueFrom(this.myObservable$.pipe(takeWhile(val => val != 5, true)))

Upvotes: 0

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