CODEWITHSUNDEEP
typescriptrxjsobservable
Trevor Murphy
Trevor Murphy

Reputation: 161

Observable nested callbacks

I have a relatively complex nested observable that switches to other observables and needs the info returned from each previous observable. Something like:

of(1).pipe(
  switchMap(res =>
    of(2).pipe(
      switchMap(res2 =>
        of(3).pipe(
          switchMap(res3 => {
              console.log(res)
              console.log(res2)
              console.log(res3)
              return of()
            }
          )
        )
      )
    )
  )
)

Is there a way to accomplish this without the nested callbacks of the switchmaps? The main issue is having to remember the value emitted from each nested observable.

Upvotes: 0

Views: 63

Answers (2)

JB Nizet
JB Nizet

Reputation: 691765

Sure. All you need to do is to reemit the previous values:

of(1).pipe(
  switchMap(res => of({ res1: res, res2: 2 })),
  switchMap(res => of({ ...res, res3: 3 })
).subscribe(...)

or

of(1).pipe(
  switchMap(res1 => of(2).pipe(map(res2 => ({ res1, res2 }))),
  switchMap(res => of(3).pipe(map(res3 => ({ ...res, res3 })))
).subscribe(...)

Upvotes: 3

Andrei Gătej
Andrei Gătej

Reputation: 11934

I think this can do the job:

of(1).pipe(
  switchMap(res => forkJoin(of(res), of(2))), // Returns [1, 2]
  switchMap(res => forkJoin(...res.map(v => of(v)), of(3))), // forkJoin(of(1), of(2), of(3))
  switchMap(res => forkJoin(...res.map(v => of(v)), of(4))),
).subscribe(console.log) // 1, 2, 3, 4]

Upvotes: 0

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