jwt.interceptor.ts

import { 
  HttpInterceptor, 
  HttpRequest, 
  HttpResponse, 
  HttpHandler, 
  HttpEvent 
} from '@angular/common/http';
import 'rxjs/add/operator/map';

@Injectable()
class JWTInterceptor implements HttpInterceptor {

  constructor(private router: Router) {}
  
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    return next.handle(req).map((event: HttpEvent<any>) => {
      if (event instanceof HttpResponse) {
        // do stuff with response if you want
      }
    }, (err: any) => {
      if (err instanceof HttpErrorResponse {
        if (err.status === 401) {
          // redirect to login
        }
      }
    });
  }
}

It does not work for me - while server returns 403 Forbidden it does not go to error callback.
Instead it triggers the successful callback and the event is typeof object (which is useless in reaction on error response). The object looks like this:
{type:0}

Could you help me with that, please?

@kuceraf

changing
return next.handle(req).map((event: HttpEvent) => {
to
return next.handle(req).do((event: HttpEvent) => {

fixed it for me. Refer to https://angular.io/guide/http#intercepting-all-requests-or-responses

@Greg5ki, thanks for posting up the .map() => .do() change, that worked perfectly for me (.map() was only executing the first success arg, not the error).