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>}`)
});
        })
        .catch(reason => {
          this._readyCapability.reject(
            new Error(`Setting up fake worker failed: "${reason.message}".`)
          );
        });
    }
    /**
     * Destroys the worker instance.
     */
    destroy() {
      this.destroyed = true;
      if (this._webWorker) {
        
        this._webWorker.terminate();
        this._webWorker = null;
      }
      pdfWorkerPorts.delete(this._port);
      this._port = null;
      if (this._messageHandler) {
        this._messageHandler.destroy();
        this._messageHandler = null;
      }
    }
    /**
     * @param {PDFWorkerParameters} params - The worker initialization
     *   parameters.
     */
    static fromPort(params) {