Why inherit express applications?

Question

Express.js

Good morning, met the design:

const app   = express();
const admin = express();

admin.get('/admin', (req, res) => {
  res.send('admin');
});

app.get('/admin', admin);

Why do this?
After all, this is what Router is for.const admin = express.Router();

Answer 1

surely then these two expresses are launched each on their own port, in the spirit of

app.listen(3000)
admin.listen(3001)