public function getAsset($asset, $extensionId = null)
    {
        if( ! is_null($extensionId)){
            $url = $this->getJsBaseWww($extensionId) . FsUtils::normalizePath($asset);
        } else {
            $url = $this->getAssetBaseUrl() . FsUtils::normalizePath($asset);
        }

        $isFolder = (substr_compare($url, '/', strlen($url) - 1) === 0);

        $buster = $this->getCacheBuster();
        if($buster != false && $isFolder == false) {
            $url .= '?' . self::BUSTER_QUERY_KEY . '=' . urlencode($buster);
        }

        return $url;
    }