Route prefixing in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing prefixed routes?

Consider this Express app code with route prefixing. What response will the client receive when requesting /api/users?

Express

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

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

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

app.listen(3000);

A The client receives an empty response with status 200.

B The client receives a 404 Not Found error.

C The client receives 'Cannot GET /users' error.

D The client receives 'User list' as the response.

💡 Hint

Remember the router is mounted on '/api', so routes inside it are prefixed.

The router is mounted with app.use('/api', router), so all routes inside the router are prefixed with '/api'. The route /users inside the router becomes /api/users. So requesting /api/users matches and returns 'User list'.

📝 Syntax

intermediate

Which option correctly prefixes routes using Express Router?

You want to prefix all routes in a router with '/admin'. Which code snippet correctly achieves this?

A router.prefix('/admin'); app.use(router);

B router.use('/admin'); app.use(router);

C app.use('/admin', router);

D app.use(router, '/admin');

💡 Hint

Check how Express mounts routers with prefixes.

In Express, to prefix routes in a router, you mount the router on the app with the prefix path: app.use('/admin', router);. Other options are invalid syntax or methods that don't exist.

🔧 Debug

advanced

Why does this prefixed route not respond as expected?

Given this code, why does a GET request to '/api/products' return 404?

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

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

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

app.listen(3000);

A The route path is missing a leading slash; it should be '/products'.

B The router is not mounted correctly on the app.

C The app.listen call is missing a callback function.

D The router.get method is used incorrectly; it should be router.post.

💡 Hint

Check the route path string syntax inside router.get.

Express route paths must start with a slash. The route is defined as 'products' instead of '/products', so it does not match '/api/products'. Adding the leading slash fixes the issue.

❓ state_output

advanced

What is the output after multiple prefixed routers?

Consider this Express app code:

const express = require('express');
const app = express();
const router1 = express.Router();
const router2 = express.Router();

router2.get('/info', (req, res) => {
  res.send('Info page');
});

router1.use('/details', router2);
app.use('/api', router1);

app.listen(3000);

What response will a GET request to /api/details/info return?

A The client receives a 404 Not Found error.

B The client receives 'Info page' as the response.

C The client receives 'Cannot GET /api/details/info' error.

D The client receives an empty response with status 200.

💡 Hint

Routers can be nested and prefixes combine.

The router2 is mounted on router1 at '/details', and router1 is mounted on app at '/api'. So the full path to router2's '/info' route is '/api/details/info'. The request matches and returns 'Info page'.

🧠 Conceptual

expert

What is the effect of mounting the same router with different prefixes?

If you mount the same Express router instance twice with different prefixes like this:

const router = express.Router();
router.get('/status', (req, res) => res.send('OK'));

app.use('/service1', router);
app.use('/service2', router);

What happens when a client requests /service2/status?

A The client receives 'OK' because the router handles requests under both prefixes.

B The server throws an error at startup due to duplicate router mounting.

C The client receives a 404 Not Found error because a router cannot be mounted twice.

D The client receives 'OK' only if the request is to '/service1/status'.

💡 Hint

Think about how Express routers work when mounted multiple times.

Express allows mounting the same router multiple times with different prefixes. The router handles requests under both prefixes independently. So /service2/status returns 'OK'.