apiRouter.js

import { Router } from 'express';

const router = Router();

router.get('/users', (err, req, res, next) => {
  res.json(someshit);
});

router.get('/activities', (err, req, res, next) => {
  res.json({message: 'look at all the room we have'});
});

// and so on

export default router;

server.js

import http from 'http';
import express from 'express';
import apiRouter from './apiRouter';
import { Router } from 'express';

const app = express();
const httpServer = http.createServer(app);

const router = Router();

router.use('/api', apiRouter);

app.use(router);

app.use( (req, res, next) => {
	res.sendFile('index.html', {
		root: 'lib/static',
		headers: {
			'Content-Type': 'text/html'
		}
	}, error => {
		if( error ) {
			next( error )
		}
	})
});

// error handling
if( !production ) {
	app.use( (err, req, res, next) => {
		console.log(err.stack);
		res.status(err.status || 500);
		res.json({
			errors: {
				message: err.message,
				error: err
			}
		});
	});
}

app.use( (err, req, res, next) => {
	res.status(err.status || 500);
	res.json({
		errors: {
			message: err.message,
			error: {}
		}
	});
});

httpServer.listen( process.env.PORT, _ => 
	console.info(`Listening on port ${httpServer.address().port}`)
);