Method addClass

frontend/src/ts/utils/dom.ts:975–980

* Add a class to all elements in the array

(className: string | string[])

   * Add a class to all elements in the array
   */
  addClass(className: string | string[]): this {
    for (const item of this) {
      item.addClass(className);
    }
    return this;
  }

  /**
   * Set innerHTML of all elements in the array