ydn-fetching-data-observable-chain.ts

requireUsers$ = this.userSelectors.needUsers$.pipe(
  filter(needUsers => needUsers),
  tap(() => this.store.dispatch({type: 'GET_USERS'})),
  switchMap(() => this.getUsers()),
  tap(users => this.store.dispatch({type: 'RECEIVE_USERS', users})),
  share(),
);

users$ = using(
  () => this.requireUsers$.subscribe(), 
  () => this.userSelectors.users$,
);

requireUsersExtraData$ = this.users$.pipe(
  withLatestFrom(this.userSelectors.needUsersExtraData$),
  filter(([users, needData]) => Boolean(users.length) && needData),
  tap(() => this.store.dispatch({type: 'GET_USERS_EXTRA_DATA'})),
  switchMap(() => this.getUsers()),
  tap(users => this.store.dispatch({
    type: 'RECEIVE_USERS_EXTRA_DATA', 
    users
  })),
  share(),
);

usersExtraData$ = using(
  () => this.requireUsersExtraData$.subscribe(),
  () => this.userSelectors.usersExtraData$,
);

I assume line 17 is supposed to call this.getExtraData() or something along those lines?