https://github.com/mozilla/pdf.js/blob/0df1a5661958df0c4ed2f73b0f3266d825c5c280/src/display/api.js#L710-L719
The return type signature `@returns {Promise<{num: number, gen: number}>}` is mismatched with its definition. (should be `@returns {Promise<number>}`)
return this._transport.getPageLabels();
  }
  /**
   * @returns {Promise<string>} A promise that is resolved with a {string}
   *   containing the page layout name.
   */
  getPageLayout() {
    return this._transport.getPageLayout();
  }
  /**
   * @returns {Promise<string>} A promise that is resolved with a {string}
   *   containing the page mode name.
   */
  getPageMode() {
    return this._transport.getPageMode();
  }
  /**
   * @returns {Promise<Object | null>} A promise that is resolved with an
   *   {Object} containing the viewer preferences, or `null` when no viewer
   *   preferences are present in the PDF file.
   */
  getViewerPreferences() {
    return this._transport.getViewerPreferences();
  }
  /**
   * @returns {Promise<any | null>} A promise that is resolved with an {Array}
   *   containing the destination, or `null` when no open action is present
   *   in the PDF.
   */
  getOpenAction() {