function getCompoundFileExtension(fullPath) {
        var baseName = FileUtils.getBaseName(fullPath),
            parts = baseName.split(".");

        // get rid of file name
        parts.shift();
        if (baseName[0] === ".") {
            // if starts with a `.`, then still consider it as file name
            parts.shift();
        }

        var extension = [parts.pop()], // last part is always an extension
            i = parts.length;
        while (i--) {
            if (getLanguageForExtension(parts[i])) {
                extension.unshift(parts[i]);
            } else {
                break;
            }
        }
        return extension.join(".");
    }
Get the file extension (excluding ".") given a path OR a bare filename.
Returns "" for names with no extension.
If the only `.` in the file is the first character,
returns "" as this is not considered an extension.
This method considers known extensions which include `.` in them.

@param {string} fullPath full path to a file or directory
@return {string} Returns the extension of a filename or empty string if
the argument is a directory or a filename with no extension