Невалидный JSON?

$('#clicked').on ('click' , function () {
            $.ajax (
                {
                    url: "",
                    method: "POST",

                    data :
                    {
                        'name': $('#clicked').text(),
                        'level': 'plus',
                    },
                    success: function (data) {

                       alert(data);
                  }

if (Yii::$app->request->isAjax) {

          if ($_POST['level']=='plus') {
              Yii::$app->response->format = Response::FORMAT_JSON;
                $level=$level+1;
                $folderLevel=$folderLevel->getFolderLevel($level,$_POST['name']);

                return $folderLevel;
           }