interceptor-response.ts

@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
      }
    }).catch(err => {
      if (err instanceof HttpErrorResponse {
          if (err.status === 401) {
             // JWT expired, go to login
             // Observable.throw(err);
          }
        }
    })
  }
}

Also, is the constructor(private router: Router) {} really needed?

@mackelito, you have to return an Observable and add a parentheses in your if.
Example:

if (err instanceof HttpErrorResponse) {
            if (err.status === 401) {
               // JWT expired, go to login
               return Observable.throw(err);
            }
          }

Your second question was "Also, is the constructor(private router: Router) {} really needed?", you dont need, but can redirect to any route like "access denied"

You're missing a closing parentheses on line 13, fixed: https://gist.github.com/SamuelMarks/fec9a736764c49b4790adbb99aca54a5