Router Base Paths

Merging Traffic Routers

We have our thingRouter.js, but app.js needs to know about it. We connect them using app.use(), and we give it a Base Path.

Fig 1: Taking the Exit.

app.js

const thingRouter = require('./routes/thingRouter');

// Mount the router
// Any request starting with "/things" goes here
app.use('/things', thingRouter);

Context Awareness

The magic here is that inside thingRouter.js, the router doesn’t know about the /things prefix. It only cares about what comes after.

Once you take the exit, you are no longer on the highway.

When we mount a router on /things, Express strips that part of the URL off before handing the request to the router.

• Request URL: /things/42
• Main App sees: /things -> passes control to thingRouter
• Router sees: /42

So inside thingRouter.js, we must REMOVE the prefix we added in the previous lesson:

routes/thingRouter.js

// OLD (Wrong inside a mounted router)
// router.get('/things', ...)

// NEW (Correct)
// Matches /things/
router.get('/', (req, res) => res.send('List of Things'));

// Matches /things/:id
router.get('/:id', (req, res) => res.send('Details of Thing'));

We’ve effectively removed the repetitive /things prefix from inside the router file.

Solo Warning

If you accidentally include /things inside the router file AND in the app.use base path, your URL becomes /things/things/42. Don’t double-dip.

---

Extra Bits & Bytes

Express Router with Base Paths - Demo Repo

Express Guide: Router

⏭ Delivery

Traffic is flowing. Now let’s talk about the cargo. How do we send a response?