Separating routes into files in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing the /users route?

Given the Express app setup below with routes separated into files, what will the server respond when a client requests /users?

Express

const express = require('express');
const app = express();
const usersRouter = require('./routes/users');

app.use('/users', usersRouter);

// routes/users.js
const express = require('express');
const router = express.Router();

router.get('/', (req, res) => {
  res.send('User list');
});

module.exports = router;

A The server throws a runtime error because of missing middleware.

B The server responds with 'Cannot GET /users'.

C The server responds with 'Welcome to users'.

D The server responds with 'User list'.

💡 Hint

Check how the router handles the / path inside the /users prefix.

The usersRouter handles requests to / relative to /users. So a GET request to /users matches router.get('/', ...) and responds with 'User list'.

📝 Syntax

intermediate

Which option correctly exports an Express router from a separate file?

Choose the correct way to export an Express router from a file named products.js.

Express

const express = require('express');
const router = express.Router();

router.get('/', (req, res) => {
  res.send('Product list');
});

// What is the correct export statement here?

A module.exports = router;

B module.export = router;

C export default router;

D exports = router;

💡 Hint

Remember how CommonJS modules export values.

In CommonJS, module.exports = router; correctly exports the router object. exports = router; only reassigns the local variable and does not change the exported object. export default is ES module syntax and not valid here. module.export is a typo.

🔧 Debug

advanced

Why does the route handler not respond when using separated routes?

Consider this Express app setup:

const express = require('express');
const app = express();
const apiRouter = require('./routes/api');

app.use('/api', apiRouter);

// routes/api.js
const express = require('express');
const router = express.Router();

router.get('/data', (req, res) => {
  // missing res.send or res.end
});

module.exports = router;

What happens when a client requests /api/data?

A The request hangs and eventually times out because no response is sent.

B The server throws a syntax error on startup.

C The server responds with an empty 200 OK response.

D The server responds with a 404 Not Found error.

💡 Hint

Check if the route handler sends a response.

The route handler does not call res.send() or res.end(), so the request stays open and the client waits indefinitely until timeout.

🧠 Conceptual

advanced

What is the benefit of separating routes into files in Express?

Why do developers separate routes into different files when building Express applications?

A To avoid using middleware functions in the main app file.

B To improve server performance by loading routes faster.

C To organize code better and keep route logic modular and maintainable.

D To prevent Express from handling requests synchronously.

💡 Hint

Think about code organization and teamwork.

Separating routes into files helps keep code organized, easier to read, and maintain. It also allows multiple developers to work on different routes without conflicts. It does not directly affect performance or middleware usage.

❓ state_output

expert

What is the output after mounting nested routers with middleware?

Given the following Express app and route files, what will be the output when a client requests /api/users/profile?

Express

const express = require('express');
const app = express();
const apiRouter = require('./routes/api');

app.use('/api', apiRouter);

// routes/api.js
const express = require('express');
const router = express.Router();
const usersRouter = require('./users');

router.use('/users', (req, res, next) => {
  req.customData = 'middleware data';
  next();
});
router.use('/users', usersRouter);

module.exports = router;

// routes/users.js
const express = require('express');
const router = express.Router();

router.get('/profile', (req, res) => {
  res.send(req.customData);
});

module.exports = router;

A The server responds with 404 Not Found because /profile route is not found.

B "middleware data" is sent as the response.

C "undefined" is sent as the response because req.customData is missing.

D The server throws an error because middleware is not properly chained.

💡 Hint

Consider how middleware modifies req and how nested routers handle requests.

The middleware on /users adds req.customData. Then the nested usersRouter handles /profile and sends req.customData. So the response is 'middleware data'.