user$ = this.http.get<User[]>(url).pipe(
tap(data => console.log(JSON.stringfy(data))),
catchError(this.handleError)
)

privat handleError(err: HttpErrorResponse): Observable<never>{
  let errorMsg = `An error occurred: ${err.error.message}`;
  console.log(err);
  return throwError(()=> errorMsg)
}