async function getExtension(fileName) {
    try {
        let extensios = ['.js', '.ts', '.jsx', '.tsx', '.mjs', '.cjs'];
        let data = fileName.split('.').slice(-1)[0].toLowerCase();
        if (extensios.includes(data)) {
            return '';
        }

        for (let idx = 0; idx < extensios.length; ++idx) {
            if (fs.existsSync(fileName + extensios[idx])) {
                return extensios[idx];
            }
        }
        return '';
    } catch (err) {
        return '';
    }
}
Get file extension.
@param {string} fileName