gistfile1.txt

  async _ensureRegionFilesDownloaded() {
    log.info("_ensureRegionFilesDownloaded");
    this._remoteSettings.on(
      "sync",
      async ({ data: { created, updated, deleted } }) => {
        log.info("_ensureRegionFilesDownloaded data synced");
        const toDelete = deleted.filter(d => d.attachment);
        const toDownload = created
          .concat(updated.map(u => u.new))
          .filter(d => d.attachment);

        // Remove local files of deleted records
        await Promise.all(
          toDelete.map(entry => this._remoteSettings.attachments.delete(entry))
        );

        // Download attachments
        log.info("_ensureRegionFilesDownloaded downloading attachments");
        await Promise.all(
          toDownload.map(entry =>
            this._remoteSettings.attachments.download(entry, {
              retries: 2,
              useCache: true,
            })
          )
        );
        this._regionFilesReady = true;
        log.info("_ensureRegionFilesDownloaded completed");
      }
    );
    await this._remoteSettings.sync();
  }