javascript - How to get RxJS Observable events in zero time?

Question

I'm collecting all the events of an Observable to a data array:

const obs$ = Rx.Observable
  .interval(500)
  .take(4);

let data = [];
const start = performance.now();

obs$.subscribe(
  value => {
    data.push({
      time: performance.now() - start,
      data: value
    });
  },
  () => {},
  () => {
    console.log(JSON.stringify(data, null, 2));
  }
);

<script src="https://unpkg.com/rxjs@5.2.0/bundles/Rx.js"></script>

Answer 1

You can create an instance of the VirtualTimeScheduler and can specify it in the call to interval.

If you then call flush on the scheduler after subscribing, the events will be emitted immediately:

const scheduler = new Rx.VirtualTimeScheduler();

const obs$ = Rx.Observable
  .interval(500, scheduler)
  .take(4);

let data = [];
const start = scheduler.now();

obs$.subscribe(
  value => {
    data.push({
      time: scheduler.now() - start,
      data: value
    });
  },
  () => {},
  () => {
    console.log(JSON.stringify(data, null, 2));
  }
);

scheduler.flush();

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://unpkg.com/rxjs@5.2.0/bundles/Rx.js"></script>