private function getScriptSrc($callbackName = null)
    {
        $queries = [];

        if ($this->hasLang()) {
            array_set($queries, 'hl', $this->lang);
        }

        if ($this->hasCallbackName($callbackName)) {
            array_set($queries, 'onload', $callbackName);
            array_set($queries, 'render', 'explicit');
        }

        return static::CLIENT_URL . (count($queries) ? '?' . http_build_query($queries) : '');
    }