PDF.js version: 3.5.141

These two properties should be marked as not mandatory as they are initialized if not present
const currentPageNumber = this._currentPageNumber;
    if (currentPageNumber <= 1) {
      return false;
    }
    const advance =
      this._getPageAdvance(currentPageNumber,  true) || 1;
    this.currentPageNumber = Math.max(currentPageNumber - advance, 1);
    return true;
  }
  /**
   * @typedef {Object} ChangeScaleOptions
   * @property {number} [drawingDelay]
   * @property {number} [scaleFactor]
   * @property {number} [steps]
   */
  /**
   * Increase the current zoom level one, or more, times.
   * @param {ChangeScaleOptions} [options]
   */
  increaseScale({ drawingDelay, scaleFactor, steps } = {}) {