public function js($name = NULL, $external = FALSE, array $options = []) {
        if ($name) {
            $this->_js[$name] = $options + [
                'src' => $external ? $name : PO_PATH_JS  . '/' . $name
            ];
        } else {
            return implode(PHP_EOL, array_map(function($value) {
                return '<script ' . Str::htmlserialize($value) . '></script>';
            }, $this->_js)) . PHP_EOL;
        }
    }