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>}`)
assert(
      args.intent,
      'PDFPageProxy._pumpOperatorList: Expected "intent" argument.'
    );
    const readableStream = this._transport.messageHandler.sendWithStream(
      "GetOperatorList",
      args
    );
    const reader = readableStream.getReader();
    const intentState = this._intentStates.get(args.intent);
    intentState.streamReader = reader;
    const pump = () => {
      reader.read().then(
        ({ value, done }) => {
          if (done) {
            intentState.streamReader = null;
            return;
          }
          if (this._transport.destroyed) {
            return; 
          }
          this._renderPageChunk(value, intentState);
          pump();