Determine if device making the request is a mobile device mobile device like
Mozilla/5.0 (Linux; U; Android 2.1; en-us; GT-I9000 Build/ECLAIR) AppleWebKit/525.10+ (KHTML, like Gecko) Version/3.0.4 Mobile Safari/523.12.2
You can use it to detect and serve a different page to the user.
Example
var mobile =require('is-mobile-browser');
mobile('Mozilla/5.0 (Linux; U; Android 2.1; en-us; GT-I9000 Build/ECLAIR) AppleWebKit/525.10+ (KHTML, like Gecko) Version/3.0.4 Mobile Safari/523.12.2');// true
mobile('Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_1 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8C148 Safari/6533.18.5');// true
mobile('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.99 Safari/537.36');// false