app.js

var bundle = require('./bundle.js')

bundle('whatever/code/you/want.js', function (err, module) {
  /* do shit, hooray */
})

bundle.js

var path = require('path')

module.exports = bundle;

function bundle(script, opts, cb) {
  if (typeof opts === 'function') {
    cb = opts;
    opts = {};
  }
  
  var mount = opts.mount || '/browser';
  
  loadScript(mount + '/' + script, function (err) {
    if (err) {
      return cb(err);
    }
    
    cb(null, window[script])
  })
}

server.js

var Router = require('routes-router')
var http = require('http')
var ServeBrowserify = require('serve-browserify')

var router = Router();

router.addRoute('/browser/*', ServeBrowserify({
  root: path.join(__dirname, 'browser'),
  base: '/browser',
  standalone: true
}))

http.createServer(router).listen(3000)