// NavBar Template
<div class="errors" *ngIf="errorInterceptor.errors.value | async">
    <div class="error"><b>prova {{errorInterceptor.errors.value}}</b></div>
</div>

//ErrorInterceptor
@Injectable()
export class ErrorInterceptor implements HttpInterceptor {
    constructor(private authenticationService: AuthenticationService, private router: Router) {}

    errors = new BehaviorSubject<string>(null);

    intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        //next.handle(request) trasforma un HttpRequest in uno stream di HttpEvents,
        //restituisce un Observable <HttpEvent> 'Union type for all possible events on the response stream.'
        return next.handle(request).pipe(catchError(err => {
            if (err.status >= 400 && err.status < 500) {
                // auto logout if 401 response returned from api
                //this.authenticationService.logout();
                //location.reload(true);
                //console.error("Error:="+err.error.msg);
                //this.router.navigate(['/login']);
                console.error('error-interceptor:error status=' + err.status);
                this.errors.next(err.error);
            } else {

                console.error('error-interceptor:err=' + err.error + ' statusText=' + err.statusText + ' status:' + err.status);
                this.errors.next(err.error);

            }

            const error = err.error.msg || err.statusText;
            return throwError(error);
        }))
    }
}