Difference Between app.use() and router.use() in Express

router.get is only for defining subpaths. Consider this example:

var router = express.Router();

app.use('/first', router); // Mount the router as middleware at path /first

router.get('/sud', smaller);

router.get('/user', bigger);

• If you open /first/sud, then the smaller function will get called.
• If you open /first/user, then the bigger function will get called.

In short, app.use('/first', router) mounts the middleware at path /first, then router.get sets the subpath accordingly.

But if we instead use the following:

app.use('/first', fun);

app.get('/sud', bigger);

app.get('/user', smaller);

• If you open /first in your browser, fun will get called,
• For /sud, bigger will get called
• For /user, smaller will get called

But remember for /first/sud, no function will get called.

This link may also help: http://expressjs.com/api.html#router