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>}`)
if (!params || !params.port) {
        throw new Error("PDFWorker.fromPort - invalid method signature.");
      }
      if (pdfWorkerPorts.has(params.port)) {
        return pdfWorkerPorts.get(params.port);
      }
      return new PDFWorker(params);
    }
    static getWorkerSrc() {
      return getWorkerSrc();
    }
  }
  return PDFWorker;
})();
/**
 * For internal use only.
 * @ignore
 */
class WorkerTransport {