How to use the rx-jupyter.kernels.list function in rx-jupyter

async checkUp(host: HostRecord): Promise {
    if (host.type !== UP) {
      return false;
    }

    return kernels
      .list(host.config)
      .pipe(
        map(xhr => {
          console.log(xhr);
          return true;
        }),
        catchError(err => {
          console.error("error listing kernels on server", err);
          return of(false);
        })
      )
      .toPromise();
  }