shortcut-manager3.ts

  private singleShortcut$(keyCodes: string[]): Observable<KeyboardEvent[] | undefined> {
    const keyEvents$: Observable<KeyboardEvent> = this.createKeyEvents();
    const pressedKeys = new Set<string>();

    // create event stream for every shortcut key
    const shortcutKeys$: Observable<KeyboardEvent>[] = keyCodes.map(keyCode => keyEvents$
      .pipe(
        filter(keyboardEvent => keyboardEvent.code === keyCode),
        tap(keyboardEvent => {
          if (keyboardEvent.type === 'keydown') {
            pressedKeys.add(keyboardEvent.code);
          } else {
            pressedKeys.delete(keyboardEvent.code);
          }
        })
      ));

    // emit only when all specified keys are pressed at the same time or released completely
    return combineLatest(shortcutKeys$)
      .pipe(
        filter(keyboardEvents => this.checkPressedKeys(keyboardEvents, pressedKeys.size)),
        map(keyboardEvents => pressedKeys.size === 0 ? undefined : keyboardEvents)
      );
  }

  private createKeyEvents(): Observable<KeyboardEvent> {
    const keydown$ = fromEvent<KeyboardEvent>(document, 'keydown');
    const keyup$ = fromEvent<KeyboardEvent>(document, 'keyup');
    return merge(keydown$, keyup$)
      .pipe(
        distinctUntilChanged((a, b) => a.code === b.code && a.type === b.type),
        share()
      );
  }