diff -u b/formatters/accordion/accordion.js b/formatters/accordion/accordion.js
--- b/formatters/accordion/accordion.js
+++ b/formatters/accordion/accordion.js
@@ -74,7 +74,7 @@
           // event is fired.
           $(document).once('fieldgroup_accordion_state_visible').bind('state:visible', function(e) {
             if ($(e.target).hasClass('field-group-child-field')) {
-              let $group = $(e.target).closest('.field-group-accordion-item')
+              let $group = $(e.target).closest('.field-group-accordion-item');
               if ($group.length !== 0) {
                 const tabId = $group.attr('aria-labelledby');
                 Drupal.FieldGroup.hideGroupIfEmpty($group, $(document).find('#' + tabId));
diff -u b/formatters/details/details.js b/formatters/details/details.js
--- b/formatters/details/details.js
+++ b/formatters/details/details.js
@@ -31,7 +31,7 @@
       // "state:visible" event is fired.
       $(document).once('fieldgroup_details_state_visible').bind('state:visible', function(e) {
         if ($(e.target).hasClass('field-group-child-field')) {
-          let $group = $(e.target).closest('.field-group-details')
+          let $group = $(e.target).closest('.field-group-details');
           if ($group.length !== 0) {
             Drupal.FieldGroup.hideGroupIfEmpty($group, null, true);
           }
diff -u b/formatters/fieldset/fieldset.js b/formatters/fieldset/fieldset.js
--- b/formatters/fieldset/fieldset.js
+++ b/formatters/fieldset/fieldset.js
@@ -32,7 +32,7 @@
       // "state:visible" event is fired.
       $(document).once('fieldgroup_fieldset_state_visible').bind('state:visible', function(e) {
         if ($(e.target).hasClass('field-group-child-field')) {
-          let $group = $(e.target).closest('.field-group-fieldset')
+          let $group = $(e.target).closest('.field-group-fieldset');
           if ($group.length !== 0) {
             Drupal.FieldGroup.hideGroupIfEmpty($group, null, true);
           }
diff -u b/formatters/tabs/tabs.js b/formatters/tabs/tabs.js
--- b/formatters/tabs/tabs.js
+++ b/formatters/tabs/tabs.js
@@ -51,7 +51,7 @@
         // fired.
         $(document).once('fieldgroup_tabs_state_visible').bind('state:visible', function(e) {
           if ($(e.target).hasClass('field-group-child-field')) {
-            let $group = $(e.target).closest('.field-group-tab')
+            let $group = $(e.target).closest('.field-group-tab');
             let $tab;
             if ($group.length !== 0) {
               if (typeof $group.data('horizontalTab') !== 'undefined') {
diff -u b/js/field_group.js b/js/field_group.js
--- b/js/field_group.js
+++ b/js/field_group.js
@@ -61,7 +61,6 @@
     }
   };
 
-
   /**
    * Behaviors.
    */
diff -u b/src/FormatterHelper.php b/src/FormatterHelper.php
--- b/src/FormatterHelper.php
+++ b/src/FormatterHelper.php
@@ -91,7 +91,6 @@
             continue;
           }
           $element[$child]['#group'] = $group_children_parent_group;
-          $element[$child]['#attributes']['class'][] = 'field-group-child-field';
         }
       }
 
@@ -100,6 +99,7 @@
               continue;
             }
             $element[$child]['#group'] = $group_children_parent_group;
+            $element[$child]['#attributes']['class'][] = 'field-group-child-field';
           }
         }
       }