I'm trying to wrap my head around how RxJS concat works, and how it works with Promises in general.

I have two observables:

currentConfirmation$ emits null

newConfirmation$ emits a new confirmation

Could someone explain why this works:

const finalConfirmation$ = currentConfirmation$.pipe(
    switchMap((conf) => {
      if (!conf) {
        return newConfirmation$
      }

      return of(conf)
    })
  )

But this does not

const finalConfirmation$ = concat(currentConfirmation$, newConfirmation$).pipe(find((conf) => !!conf))

By not works I mean this test passes with the switchMap version and times out with the concat version

test("updateConfirmation should create the confirmation if it doesn't exist", (done) => {
    updateConfirmation({ value: true, symbol: 'LTCUSD', name: 'LTC_TEST_CONFIRMATION_999' }).subscribe((conf) => {
      expect(conf.entityData).toEqual({ value: true, symbol: 'LTCUSD', name: 'LTC_TEST_CONFIRMATION_999' })
      done()
    })
  })

I would also love to know if there is a better approach to accomplishing the above than what I have come up with.

Edit: Here is all the relevant code for the test:

export const confirmationRepository$ = client$.pipe(
  switchMap(async (client) => client.fetchRepository(schema)),
  delayWhen((cr) => from(cr.createIndex())),
  shareReplay(1)
)

export const updateConfirmation = (newData: Partial<Confirmation>) => {
  // TODO: Just don't process the search if we get empty strings
  const currentConfirmation$ = getConfirmation(newData.symbol || ' ', newData.name || ' ')
  const newConfirmation$ = createConfirmation(newData)

  // const finalConfirmation$ = concat(currentConfirmation$, newConfirmation$).pipe(find((conf) => !!conf))
  const finalConfirmation$ = currentConfirmation$.pipe(
    switchMap(async (conf) => {
      if (!conf) {
        return newConfirmation$
      }
      return of(conf)
    }),
    concatAll(),
    combineLatestWith(confirmationRepository$),
    concatMap(async ([conf, confRepo]) => {
      conf.value = !!newData.value
      await confRepo.save(conf)
      return conf
    })
  )

  return finalConfirmation$
}

export const getConfirmation = (symbol: string, name: string) => {
  return confirmationRepository$.pipe(
    switchMap((cr) => cr.search().where('symbol').equals(symbol).and('name').equals(name).first())
  )
}

export const getConfirmations = (symbol: string) => {
  return confirmationRepository$.pipe(switchMap((cr) => cr.search().where('symbol').equals(symbol).returnAll()))
}