gistfile1.js

  async _ensureRegionFilesSynced() {
    log.info("_ensureRegionFilesSynced");
    this._remoteSettings.on("sync", async ({ data: { deleted } }) => {
      log.info("_ensureRegionFilesSynced sync event");
      const toDelete = deleted.filter(d => d.attachment);
      // Remove local files of deleted records
      await Promise.all(
        toDelete.map(entry => this._remoteSettings.attachments.delete(entry))
      );
      this._ensureRegionFilesDownloaded();
    });
  }

  async _ensureRegionFilesDownloaded() {
    log.info("_ensureRegionFilesDownloaded");
    let records = this._remoteSettings.get();
    await Promise.all(
      records.map(entry =>
        this._remoteSettings.attachments.download(entry, {
          retries: 2,
          useCache: true,
        })
      )
    );
    log.info("_ensureRegionFilesDownloaded complete");
    this._regionFilesReady = true;
  }

  async _getPlainMap() {
    return this._fetchAttachment("world");
  }

  async _getBufferedMap() {
    return this._fetchAttachment("world-buffered");
  }

  async _fetchAttachment(id) {
    let record = (await this._remoteSettings.get({ filters: { id } })).pop();
    let url = await this._remoteSettings.attachments.download(record);
    let req = await fetch(url);
    return req.json();
  }