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>}`)
length,
    initialData,
    progressiveDone = false,
    contentDispositionFilename = null
  ) {
    this.length = length;
    this.initialData = initialData;
    this.progressiveDone = progressiveDone;
    this.contentDispositionFilename = contentDispositionFilename;
    this._rangeListeners = [];
    this._progressListeners = [];
    this._progressiveReadListeners = [];
    this._progressiveDoneListeners = [];
    this._readyCapability = createPromiseCapability();
  }
  addRangeListener(listener) {
    this._rangeListeners.push(listener);
  }
  addProgressListener(listener) {
    this._progressListeners.push(listener);
  }
  addProgressiveReadListener(listener) {
    this._progressiveReadListeners.push(listener);
  }
  addProgressiveDoneListener(listener) {