yii\web\JsonResponseFormatter::formatJsonp PHP Method

    protected function formatJsonp($response)
    {
        $response->getHeaders()->set('Content-Type', 'application/javascript; charset=UTF-8');
        if (is_array($response->data) && isset($response->data['data'], $response->data['callback'])) {
            $response->content = sprintf('%s(%s);', $response->data['callback'], Json::htmlEncode($response->data['data']));
        } elseif ($response->data !== null) {
            $response->content = '';
            Yii::warning("The 'jsonp' response requires that the data be an array consisting of both 'data' and 'callback' elements.", __METHOD__);
        }
    }