RxJs: poll until interval done or correct data received

Question

How do i execute the following scenario in the browser with RxJs:

• submit data to queue for processing
• get back the job id
• poll another endpoint e

Answer 1

Not your question, but I needed the same functionality

import { takeWhileInclusive } from 'rxjs-take-while-inclusive'
import { of, interval, race, throwError } from 'rxjs'
import { catchError, timeout, mergeMap, delay, switchMapTo } from 'rxjs/operators'

const defaultMaxWaitTimeMilliseconds = 5 * 1000

function isAsyncThingSatisfied(result) {
  return true
}

export function doAsyncThingSeveralTimesWithTimeout(
  doAsyncThingReturnsPromise,
  maxWaitTimeMilliseconds = defaultMaxWaitTimeMilliseconds,
  checkEveryMilliseconds = 500,
) {
  const subject$ = race(
    interval(checkEveryMilliseconds).pipe(
      mergeMap(() => doAsyncThingReturnsPromise()),
      takeWhileInclusive(result => isAsyncThingSatisfied(result)),
    ),
    of(null).pipe(
      delay(maxWaitTimeMilliseconds),
      switchMapTo(throwError('doAsyncThingSeveralTimesWithTimeout timeout'))
    )
  )

  return subject$.toPromise(Promise) // will return first result satistieble result of doAsyncThingReturnsPromise or throw error on timeout
}

Example

// mailhogWaitForNEmails
import { takeWhileInclusive } from 'rxjs-take-while-inclusive'
import { of, interval, race, throwError } from 'rxjs'
import { catchError, timeout, mergeMap, delay, switchMap } from 'rxjs/operators'

const defaultMaxWaitTimeMilliseconds = 5 * 1000

export function mailhogWaitForNEmails(
  mailhogClient,
  numberOfExpectedEmails,
  maxWaitTimeMilliseconds = defaultMaxWaitTimeMilliseconds,
  checkEveryMilliseconds = 500,
) {
  let tries = 0

  const mails$ = race(
    interval(checkEveryMilliseconds).pipe(
      mergeMap(() => mailhogClient.getAll()),
      takeWhileInclusive(mails => {
        tries += 1
        return mails.total < numberOfExpectedEmails
      }),
    ),
    of(null).pipe(
      delay(maxWaitTimeMilliseconds),
      switchMap(() => throwError(`mailhogWaitForNEmails timeout after ${tries} tries`))
    )
  )

  // toPromise returns promise which contains the last value from the Observable sequence.
  // If the Observable sequence is in error, then the Promise will be in the rejected stage.
  // If the sequence is empty, the Promise will not resolve.
  return mails$.toPromise(Promise)
}

// mailhogWaitForEmailAndClean
import { mailhogWaitForNEmails } from './mailhogWaitForNEmails'

export async function mailhogWaitForEmailAndClean(mailhogClient) {
  const mails = await mailhogWaitForNEmails(mailhogClient, 1)

  if (mails.count !== 1) {
    throw new Error(
      `Expected to receive 1 email, but received ${mails.count} emails`,
    )
  }

  await mailhogClient.deleteAll()

  return mails.items[0]
}