Method A.js

//Controller module
var express = require('express');
var router = express.Router();

app.route('/book')
  .get(function(req, res) {
    res.send('Get a random book');
  })
  .post(function(req, res) {
    res.send('Add a book');
  })
  .put(function(req, res) {
    res.send('Update the book');
  });
  
  module.exports = router;
  
//routs.js...?

Method B.js

const controller = {
	getBooks: function(req, res) {
	  res.send('get a random book');
	},
	
	addBook: function(req, res) {
	  res.send('add a book')
	},
	
	updateBook: function(req, res) {
	  res.send('update book')
	}
};
module.export = controller;

//route.js
const controller = require('./controller.js');

app.route('/book')
  .get(function(req, res) {
    controller.getBooks(req,res);
  })
  .post(function(req, res) {
    controller.addBook(req,res);
  })
  .put(function(req, res) {
    controller.updateBook(req,res);
  });