import { fromEvent, of } from 'rxjs';
import { mergeMap, delay, takeUntil } from 'rxjs/operators';
​
const mousedown$ = fromEvent(document, 'mousedown');
const mouseup$ = fromEvent(document, 'mouseup');
​
mousedown$
  .pipe(
    mergeMap(event =>
      of(event).pipe(
        delay(700),
        takeUntil(mouseup$)
      )
    )
  )
  .subscribe(event => console.log('Long Press!', event));

// RxJS v6+
import { of, merge } from 'rxjs';
import { mapTo, delay } from 'rxjs/operators';
​
//emit one item
const example = of(null);
//delay output of each by an extra second
const message = merge(
  example.pipe(mapTo('Hello')),
  example.pipe(
    mapTo('World!'),
    delay(1000)
  ),
  example.pipe(
    mapTo('Goodbye'),
    delay(2000)
  ),
  example.pipe(
    mapTo('World!'),
    delay(3000)
  )
);
//output: 'Hello'...'World!'...'Goodbye'...'World!'
const subscribe = message.subscribe(val => console.log(val));