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 (fakeWorkerCapability) {
      return fakeWorkerCapability.promise;
    }
    fakeWorkerCapability = createPromiseCapability();
    const loader = async function () {
      const mainWorkerMessageHandler = getMainThreadWorkerMessageHandler();
      if (mainWorkerMessageHandler) {
        
        return mainWorkerMessageHandler;
      }
      if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")) {
        const worker = await import("pdfjs/core/worker.js");
        return worker.WorkerMessageHandler;
      }
      if (
        PDFJSDev.test("GENERIC") &&
        isNodeJS &&
        
        typeof __non_webpack_require__ === "function"
      ) {