Serve different content to mobile users?

I intend for my nodejs/express app to be used by mobile users only, with dekstop users receiving completely different content. How can I detect if the client is on a mobile device or not? Anyone know of any well maintained libraries that does this?

You can write a middleware to check req.headers['user-agent'] or use express-device.

Im no expert but found this php string to work perfectly !

 <?php
  function isMobile() {
    return preg_match("/(android|avantgo|blackberry|bolt|boost|cricket|docomo|fone|hiptop|mini|mobi|palm|phone|pie|tablet|up\.browser|up\.link|webos|wos)/i", $_SERVER["HTTP_USER_AGENT"]);
 }
 if(isMobile())
    print "this is mobile yes";
 else
    print "this is mobile not true at all";
 ?>