AssetManager\View\Helper\Asset::elaborateFilePath PHP Method

    private function elaborateFilePath($filename, $queryString)
    {
        $asset = $this->assetManagerResolver->resolve($filename);
        if ($asset !== null) {
            // append last modified date to the filepath and use a custom query string
            return $this->appendTimestamp($filename, $queryString, $asset->getLastModified());
        }
        return $filename;
    }