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>}`)
loadingTask.onProgress({
                loaded: evt.loaded,
                total: evt.total,
              });
            }
          };
        }
        headersCapability.resolve({
          isStreamingSupported: fullReader.isStreamingSupported,
          isRangeSupported: fullReader.isRangeSupported,
          contentLength: fullReader.contentLength,
        });
      }, headersCapability.reject);
      return headersCapability.promise;
    });
    messageHandler.on("GetRangeReader", (data, sink) => {
      assert(
        this._networkStream,
        "GetRangeReader - no `IPDFStream` instance available."
      );
      const rangeReader = this._networkStream.getRangeReader(
        data.begin,
        data.end
      );