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; 
          }
          throw readyReason;
        });
      };
    });
    messageHandler.on("GetDoc", ({ pdfInfo }) => {
      this._numPages = pdfInfo.numPages;
      loadingTask._capability.resolve(new PDFDocumentProxy(pdfInfo, this));
    });
    messageHandler.on("DocException", function (ex) {
      let reason;
      switch (ex.name) {
        case "PasswordException":
          reason = new PasswordException(ex.message, ex.code);
          break;
        case "InvalidPDFException":
          reason = new InvalidPDFException(ex.message);
          break;
        case "MissingPDFException":
          reason = new MissingPDFException(ex.message);
          break;
        case "UnexpectedResponseException":
          reason = new UnexpectedResponseException(ex.message, ex.status);
          break;
        case "UnknownErrorException":
          reason = new UnknownErrorException(ex.message, ex.details);
          break;
      }
      if (!(reason instanceof Error)) {