Rx photobooth, take 4 photos with a 5 seconds countdown between them

rx_photobooth.js

const takePhoto = () => new Promise((resolve) => (setTimeout(resolve, Math.random() * 1E3 + 5E2, 'photo')))

const makeCountdown = (seconds) =>
	Rx.Observable
    .concat(
      Rx.Observable
        .interval(1E3)
        .take(seconds),
      Rx.Observable.defer(() => takePhoto())
    )

Rx.Observable
  .range(1, 4)
  .concatMap(() => makeCountdown(5))