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>}`)
if (!this.pendingCleanup) {
      return false;
    }
    for (const { renderTasks, operatorList } of this._intentStates.values()) {
      if (renderTasks.size > 0 || !operatorList.lastChunk) {
        return false;
      }
    }
    this._intentStates.clear();
    this.objs.clear();
    this._annotationsPromise = null;
    this._jsActionsPromise = null;
    this._xfaPromise = null;
    this._structTreePromise = null;
    if (resetStats && this._stats) {
      this._stats = new StatTimer();
    }
    this.pendingCleanup = false;
    return true;
  }
  /**
   * @private
   */
  _startRenderPage(transparency, intent) {