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>}`)
const msg = "DocException - expected a valid Error.";
        if (
          typeof PDFJSDev === "undefined" ||
          PDFJSDev.test("!PRODUCTION || TESTING")
        ) {
          unreachable(msg);
        } else {
          warn(msg);
        }
      }
      loadingTask._capability.reject(reason);
    });
    messageHandler.on("PasswordRequest", exception => {
      this._passwordCapability = createPromiseCapability();
      if (loadingTask.onPassword) {
        const updatePassword = password => {
          this._passwordCapability.resolve({
            password,
          });
        };
        try {
          loadingTask.onPassword(updatePassword, exception.code);
        } catch (ex) {
          this._passwordCapability.reject(ex);
        }
      } else {
        this._passwordCapability.reject(
          new PasswordException(exception.message, exception.code)
        );
      }