Source: modules/media_library/js/media_library.widget.es6.js

/**
 * @file media_library.widget.es6.js
 */
(($, Drupal, Sortable) => {
  /**
   * Allows users to re-order their selection with drag+drop.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Attaches behavior to re-order selected media items.
   */
  Drupal.behaviors.MediaLibraryWidgetSortable = {
    attach(context) {
      // Allow media items to be re-sorted with drag+drop in the widget.
      const selection = context.querySelectorAll('.js-media-library-selection');
      selection.forEach((widget) => {
        Sortable.create(widget, {
          draggable: '.js-media-library-item',
          handle: '.js-media-library-item-preview',
          onEnd: () => {
            $(widget)
              .children()
              .each((index, child) => {
                $(child).find('.js-media-library-item-weight').val(index);
              });
          },
        });
      });
    },
  };

  /**
   * Allows selection order to be set without drag+drop for accessibility.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Attaches behavior to toggle the weight field for media items.
   */
  Drupal.behaviors.MediaLibraryWidgetToggleWeight = {
    attach(context) {
      const strings = {
        show: Drupal.t('Show media item weights'),
        hide: Drupal.t('Hide media item weights'),
      };
      $('.js-media-library-widget-toggle-weight', context)
        .once('media-library-toggle')
        .on('click', (e) => {
          e.preventDefault();
          $(e.currentTarget)
            .toggleClass('active')
            .text(
              $(e.currentTarget).hasClass('active')
                ? strings.hide
                : strings.show,
            )
            .closest('.js-media-library-widget')
            .find('.js-media-library-item-weight')
            .parent()
            .toggle();
        })
        .text(strings.show);
      $('.js-media-library-item-weight', context)
        .once('media-library-toggle')
        .parent()
        .hide();
    },
  };

  /**
   * Disable the open button when the user is not allowed to add more items.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Attaches behavior to disable the media library open button.
   */
  Drupal.behaviors.MediaLibraryWidgetDisableButton = {
    attach(context) {
      // When the user returns from the modal to the widget, we want to shift
      // the focus back to the open button. If the user is not allowed to add
      // more items, the button needs to be disabled. Since we can't shift the
      // focus to disabled elements, the focus is set back to the open button
      // via JavaScript by adding the 'data-disabled-focus' attribute.
      $('.js-media-library-open-button[data-disabled-focus="true"]', context)
        .once('media-library-disable')
        .each(function () {
          $(this).focus();

          // There is a small delay between the focus set by the browser and the
          // focus of screen readers. We need to give screen readers time to
          // shift the focus as well before the button is disabled.
          setTimeout(() => {
            $(this).attr('disabled', 'disabled');
          }, 50);
        });
    },
  };
})(jQuery, Drupal, Sortable);