express-test.js

const express = require('express');
const app = express();

const router = express.Router();
router.get('/foo', (req, res, next) => {
  res.locals.foo = 'bar';
  next();
});
router.get('/bar', (req, res, next) => {
  res.locals.bar = 'foo';
  next();
});

app.use(router);
app.use((req, res) => {
  res.json(res.locals);
});

app.listen(3000);