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.startCleanup(keepLoadedFonts || this.isPureXfa);
  }
  /**
   * Destroys the current document instance and terminates the worker.
   */
  destroy() {
    return this.loadingTask.destroy();
  }
  /**
   * @type {DocumentInitParameters} A subset of the current
   *   {DocumentInitParameters}, which are either needed in the viewer and/or
   *   whose default values may be affected by the `apiCompatibilityParams`.
   */
  get loadingParams() {
    return this._transport.loadingParams;
  }
  /**
   * @type {PDFDocumentLoadingTask} The loadingTask for the current document.
   */
  get loadingTask() {
    return this._transport.loadingTask;
  }
  /**
   * @returns {Promise<Uint8Array>} A promise that is resolved with a
   *   {Uint8Array} containing the full data of the saved document.
   */
  saveDocument() {