Just the map so far.

users.effects.ts

// I'm the map! 🎵
const cache = new Map();

@Injectable()
export class UsersEffects {
  loadUsers$ = createEffect(() =>
    this.actions$.pipe(
      ofType(UsersActions.loadUsers),
      switchMap((action) => {
        const callable = this.fns.httpsCallable(USER_ENDPOINT);
        const reqPayload = {
          op: 'list',
          startAfter: action.cursorId,
          length: action.pageSize
        };

        return callable(reqPayload).pipe(
          map((response) => UsersActions.loadUsersSuccess({ users: response.users }))
        );
      })
    )
  );

  constructor(
    private actions$: Actions,
    private fns: AngularFireFunctions
  ) {}
}