PDF.js version: 3.5.141

These two properties should be marked as not mandatory as they are initialized if not present
return this._spreadMode;
  }
  /**
   * @param {number} mode - Group the pages in spreads, starting with odd- or
   *   even-number pages (unless `SpreadMode.NONE` is used).
   *   The constants from {SpreadMode} should be used.
   */
  set spreadMode(mode) {