return (state$: Observable<AppState>) => state$
     .select(s => s.cart);

 // Uses Observable.forkJoin() to run multiple concurrent http.get() requests.
 // The entire operation will result in an error state if any single request fails.
 getBooksAndMovies() {
     return Observable.forkJoin(
     this.http.get('/api/books'),
     this.http.get('/api/movies')
     );
 }

this.notesDataService.getNotes().mergeMap(notes => Observable.from(notes)).subscribe(note => {

 getErrorMessage: () => Observable.of('incorrect password'),

export function getLang(state$: Observable<IMultilingualState>) {
  return state$.select(state => state.lang);
}

    /**
     * Error handler
     * @param error
     * @returns { ErrorObservable }
     * @private
     */
    private _handleError (error: Response) {
        let errorMessage = error.text() || 'Server error';

        console.error(errorMessage);
        return Observable.throw(new Error(errorMessage));
    }

 .catch((error: any) => {
     console.error(error);
     return Observable.throw(error.json().error || 'Server error');
 })

 get: job => Observable.of()

 return (state$: Observable<SearchState>) => state$
   .select(s => s.loading);

 save(entity) {
     return Observable.of(entity);
 }