https://medium.com/@hendrikwallbaum/polling-using-rxjs-54f23eb78ded

Polling using RxJS

import { timer, from } from 'rxjs'
import { map, concatMap, filter, take } from 'rxjs/operators'
pollUntilTaskFinished(taskId) {
  timer(0, 500)
    .pipe(concatMap(() => from(fetch(`/tasks/${taskId}`))
      .pipe(map(response => response.json())))
    )
    .pipe(filter(backendData => backendData.processing === false))
    .pipe(take(1))
    .subscribe(() => pollingFinishedFor(taskId))
}