user-agent-express.js

/** NodeJS with Express */
var express = require('express')
  , http = require('http')
  , app = express();

http.createServer(app).listen(3000);

app.get('/', function(req, res) {
    console.log(req.get('user-agent'));
});

user-agent-match.js

/** User-agent pattern matching */
var browser = 'unknown'
  , version = 'unknown'
  , patterns = {
      android:    /android\s([0-9.]*)/i
      chrome:     /chrome\/([0-9.]*)/i,
      firefox:    /firefox\/([0-9.]*)/i,
      ie:         /msie\s([0-9.]*)/i,
      ipad:       /ipad.version\/([0-9.]*).safari/i,
      iphone_4:   /iphone\sos\s4.version.mobile\/([0-9.]*).safari/i,
      iphone_5:   /iphone\sos\s5.version.mobile\/([0-9.]*).safari/i,
      safari:     /version\/([0-9.]*).safari/i
    }
  , key, matches;

for (key in patterns) {

  matches = navigator.userAgent.match(patterns[key]);

  if (matches) {
    browser = key;
    version = matches[1];
    break;
  }
}

console.log(browser, version);

user-agent-node.js

/** Native NodeJS */
var http = require('http')
  , server = http.createServer(function(req) {
      console.log(req.headers['user-agent']);
    });

server.listen(3000, 'localhost');