public function error($fieldName, $str)
    {
        // by using this hook you can overwrite default behavior of this method
        if ($this->hookHasCallbacks('displayError')) {
            return $this->hook('displayError', [$fieldName, $str]);
        }

        $jsError = [$this->js()->form('add prompt', $fieldName, $str)];

        return $jsError;
    }