[RxJS] Groupby operator

import { Observable, fromEvent, Subject, EMPTY } from ‘rxjs‘;
import { tap, mergeMap, groupBy, timeoutWith, ignoreElements, switchMap } from ‘rxjs/operators‘;

const actions$ = dispatcher.asObservable().pipe(
  // optimize ui rendering
  tap(({ movieId }) => setButtonEmoji(movieId)),
  // group all the request by movieId
  groupBy(
    movie => movie.movieId,
    movie => movie,
    // cancel the extra requests to prevent memory leak by set 15s idel time
    actionsByGroup$ =>
      actionsByGroup$.pipe( 
        timeoutWith(15000, EMPTY),
        ignoreElements()
      )
  ),
  // for each group of request, we apply switchMap to cancel previous request
  // finally flatten the requests into one
  mergeMap(group$ => group$.pipe(switchMap(movie => toggleStatus(movie.movieId))))
);