const tradeMaxPrice$ = stratFeed$
      .pipe(
        skipUntil(stratState$.pipe(
          pluck('order'),
          filter((x) => x.type === 'buy'),
          takeUntil(stratState$.pipe(
            pluck('order'),
            filter((x) => x.type === 'sell'),
          )),
        )),
        scan((acc, curr: Feed) => {
          return (acc > curr.price) ? acc : curr.price;
        }, 0),
        tap(x => {
          this.programmaticCommandSubject.next({tradeMaxPrice: x});
        })
      );

queryBooks = (payload?) => {
    return this.store.dispatch(
        {type: Commands.QUERY_BOOKS, payload}
     );
  }

 @Effect()
  queryBooks$ = this.actions$
    .pipe(
      ofType(Commands.QUERY_BOOKS),
      switchMap(_ => this.service.queryBooks()
        .pipe(
          map((res) => this.events.queryBooksComplete(res)),
          catchError(err => this.events.queryBooksError(err))
        )));

queryBooksComplete = (payload) => {
    return {type: Events.QUERY_BOOKS_COMPLETE, payload};
};

queryBooksError = (payload) => {
    return of({type: Events.QUERY_BOOKS_COMPLETE, payload, error: true});
};

switch (event.type) {
    case Events.QUERY_BOOKS_COMPLETE: {
      return queryBooksSnapshot(state, event);
    }
     
    default: {
      return state;
    }
}

const queryBooksSnapshot = (state: IBook[], event): IBook[]  => {
   const newBooks = event.error ? [] : event.payload;
   return [...state, ...newBooks];
};

  queryBooks$(): Observable<IBook[]> {
    return this.store.select('books');
  }

export interface AppState {
  books: IBook[];
}

export const reducers: ActionReducerMap<AppState> = {
  books: fromBooks.getReducers
};

books$: Observable<IBook[]> = this.bookProj.queryAll$();

<li *ngFor="let book of books$ | async">{{book.name}}</li>