D8_rplf/core/misc/details-aria.js

/**
 * @file
 * Add aria attribute handling for details and summary elements.
 */

(function ($, Drupal) {

  'use strict';

  /**
   * Handles `aria-expanded` and `aria-pressed` attributes on details elements.
   *
   * @type {Drupal~behavior}
   */
  Drupal.behaviors.detailsAria = {
    attach: function () {
      $('body').once('detailsAria').on('click.detailsAria', 'summary', function (event) {
        var $summary = $(event.currentTarget);
        var open = $(event.currentTarget.parentNode).attr('open') === 'open' ? 'false' : 'true';

        $summary.attr({
          'aria-expanded': open,
          'aria-pressed': open
        });
      });
    }
  };

})(jQuery, Drupal);