onSubscribe = (error: ?Error, resp: WatchmanSubscribeResponse) => {
      if (error) {
        onError(error);
        return;
      }
      debug('Received subscribe response: %s', resp.subscribe);

      handleWarning(resp);

      if (resp['asserted-states'] != null) {
        this.#deferringStates = new Set(resp['asserted-states']);
      }

      onReady();
    }
Run the watchman `watch` command on the root and subscribe to changes.