loader.js

var setRoute = function(file){
	var module = require("./controller/" + file)
	module.map(function(route, index){
		routes.set(route.path, route.method, function(req, res, next){

			module[index].action(req.params, function(data, code){
        
				res.send(code, data)

				return next()
			})
		})
	})
}

fs.readdir('./controller', function(err, files){
	files.map(function(file){
		setRoute(file)
	})
})

Não testei, mas refatorei.

const setRoute = (file) => {
  const module = require("./controller/" + file)

  module.map((route, index) => routes.set(route.path, route.method, 
    (req, res, next) => module[index].action(req.params, 
      (data, code) => {
        res.send(code, data)
        return next()
      })
    )
  )
}

fs.readdir('./controller', (err, files) => 
  files.map((file) => setRoute(file)))