How to redirect on the mobile or desktop version ?

https://www.npmjs.org/package/mobile-detect

app.get('*', function (req, res) {
 md = new MobileDetect(req.headers['user-agent']);
 if (md.mobile() != null) {
  res.writeHead(301,
   {Location: 'http://m.gymbirds.com'}
  );
  res.end();
  console.log('mobile');
 }
 else {
  res.sendfile(__dirname + '/' + req.path);
  console.log('desktop');
 }
});