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));