express routers

As apps grow, the number of routes can balloon. More than that, you may need custom middleware for certain routes and not others - whether that’s a different logger, authentication, or something else.

Express makes it easy to separate out routes by defining them within a Router and then mounting the router back to the main application.

The convention is to call the main Express application, app - and it’s defined as const app = express().

In the example below, we create a separate router, with a cors middleware that’s not present on the main app.

We then mount the router on the /api path.

export const app = express()

const port = process.env.PORT || 3000

app.disable('x-powered-by')

app.use(json())
app.use(urlencoded({ extended: true }))
app.use(morgan('dev'))

app.get('/' (req, res) => {
  res.send({ data: 'root router' })
})

const router = express.Router()
router.use(cors())
router.get('/', (req, res) => {
  res.send({ data: 'api router' })
})

app.use('api', router)

If I were to start this server and send a GET request to the root, I would get the JSON object { data: 'root router'} in response. However, if I were to do the same request, but to the /api route, I would receive { data: 'api router' } because I mounted the router to the api path.

More commonly, you will see routers split into separate files and then imported back in - but for this simple example, I thought it was easier to see it all on one page.