D8_rplf/modules/field_group/formatters/tabs/tabs.js

(function ($) {

  'use strict';

  Drupal.FieldGroup = Drupal.FieldGroup || {};
  Drupal.FieldGroup.Effects = Drupal.FieldGroup.Effects || {};

  /**
   * Implements Drupal.FieldGroup.processHook().
   */
  Drupal.FieldGroup.Effects.processTabs = {
    execute: function (context, settings, group_info) {

      if (group_info.context === 'form') {

        // Add required fields mark to any element containing required fields
        var direction = group_info.settings.direction;
        $(context).find('[data-' + direction + '-tabs-panes] details').once('fieldgroup-effects').each(function () {

          var $this = $(this);
          if (typeof $(this).data(direction + 'Tab') !== 'undefined') {

            if ($this.is('.required-fields') && ($this.find('[required]').length > 0 || $this.find('.form-required').length > 0)) {
              $this.data(direction + 'Tab').link.find('strong:first').addClass('form-required');
            }

            if ($('.error', $this).length) {
              $this.data(direction + 'Tab').link.parent().addClass('error');
              Drupal.FieldGroup.setGroupWithfocus($this);
              $this.data(direction + 'Tab').focus();
            }
          }
        });

      }
    }
  };

})(jQuery, Modernizr);