RxJS - detect long mousedown

Question

I want to detect when mousedown is being fired for longer than 500ms, if so - do something. My attempt:

const button = document.querySelector('button')
const stream = Rx.Observable.fromEvent(button, 'mousedown')
const mouseUp$ = Rx.Observable.fromEvent(button, 'mouseup')
stream.delay(500).takeUntil(mouseUp$).subscribe(() => console.log(1))

It works but only the first time it runs. Then, the stream is cancelled due to takeUntil operator. How to make it work everytime?

DEMO

Answer 1

Start a TimerObservable for 500ms on every mouseDown$ event. If mouseUp$ get's fired within 500ms unsubscribe from TimerObservable.

const button = document.querySelector('button')
const mouseDown$ = Rx.Observable.fromEvent(button, 'mousedown')
const mouseUp$ = Rx.Observable.fromEvent(button, 'mouseup')

const stream$ = mouseDown$.switchMap(() => Rx.Observable.TimerObservable(500).takeUntil(mouseUp$));

stream$.subscribe(() => console.log('Only Fired after 500ms'))

RxJS >= 6.0.0

import { switchMap, takeUntil } from 'rxjs/operators';
import { timer, fromEvent } from 'rxjs';

const button = document.querySelector('button')
const mouseDown$ = fromEvent(button, 'mousedown')
const mouseUp$ = fromEvent(button, 'mouseup')

const stream$ = mouseDown$.pipe(
  switchMap(() => timer(500).pipe(takeUntil(mouseUp$)))
);

stream$.subscribe(() => console.log('Only Fired after 500ms'))

Answer 2

Example of directive for mouse hold:

@Directive({ selector: "[appMouseHold]" })
export class MouseHoldDirective implements OnInit, OnDestroy {
  @Input() set appMouseHold(tick: string | number) {
    if (typeof tick === 'string') {
      tick = parseInt(tick, 10);
    }
    
    this.tick = tick || 500;
  }
  private tick: number;
  private readonly _stop = new Subject<void>();
  private readonly _start = new Subject<void>();
  private subscription: Subscription;

  @Output() mousehold = new EventEmitter<number>();
  @Output() mouseholdstart = new EventEmitter<void>();
  @Output() mouseholdend = new EventEmitter<void>();

  ngOnInit() {
    this.subscription = this._start
      .pipe(
        tap(() => this.mouseholdstart.emit()),
        switchMap(() =>
          timer(500, this.tick).pipe(
            takeUntil(this._stop.pipe(tap(() => this.mouseholdend.emit())))
          )
        )
      )
      .subscribe((tick) => {
        this.mousehold.emit(tick);
      });
  }

  ngOnDestroy() {
    this.subscription.unsubscribe();
  }

  @HostListener("mousedown", ["$event"])
  onMouseDown($event) {
    if ($event.button === 0) {
      this._start.next();
    }
  }

  @HostListener("mouseup")
  onMouseUp() {
    this._stop.next();
  }
}

See Stackblitz

For non-angular usage you can simply replace @HostListener handlers with fromEvent() observables