Namespaces for separation in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing routes with namespaces?

Consider this Express app code that uses namespaces (routers) to separate routes:

const express = require('express');
const app = express();

const apiRouter = express.Router();
apiRouter.get('/users', (req, res) => res.send('API Users'));

const adminRouter = express.Router();
adminRouter.get('/users', (req, res) => res.send('Admin Users'));

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

app.listen(3000);

What will be the response when a client requests GET /admin/users?

Express

const express = require('express');
const app = express();

const apiRouter = express.Router();
apiRouter.get('/users', (req, res) => res.send('API Users'));

const adminRouter = express.Router();
adminRouter.get('/users', (req, res) => res.send('Admin Users'));

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

app.listen(3000);

A The response is 'Admin Users'.

B The response is 'API Users'.

C 404 Not Found error.

D 500 Internal Server Error.

💡 Hint

Think about how the app.use prefixes the routes in each router.

The adminRouter is mounted at /admin. So the route /users inside adminRouter becomes /admin/users. When the client requests /admin/users, the handler in adminRouter responds with 'Admin Users'.

📝 Syntax

intermediate

Which option correctly creates a namespace router in Express?

Which code snippet correctly creates a router namespace for /blog in Express?

A const blogRouter = express.Router; app.use('/blog', blogRouter);

B const blogRouter = new express.Router(); app.use('/blog', blogRouter);

C const blogRouter = express(); app.use('/blog', blogRouter);

D const blogRouter = express.Router(); app.use('/blog', blogRouter);

💡 Hint

Remember how to create a router instance in Express.

The correct way to create a router is by calling express.Router(). Option D does this correctly. Option D calls express() which creates an app, not a router. Option D misses parentheses, so it references the function but does not call it. Option D tries to use new which is not how Router is instantiated.

🔧 Debug

advanced

Why does this namespaced route not respond as expected?

Given this Express code:

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

userRouter.get('/profile', (req, res) => res.send('User Profile'));

app.use('/user', userRouter);

app.listen(3000);

When requesting GET /profile, the server responds with 404. Why?

Express

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

userRouter.get('/profile', (req, res) => res.send('User Profile'));

app.use('/user', userRouter);

app.listen(3000);

A Because the route is mounted under '/user', so '/profile' is not matched; the correct path is '/user/profile'.

B Because the route handler is missing a next() call.

C Because the router was not attached with app.use().

D Because the server is not listening on port 3000.

💡 Hint

Check the full path the route is mounted on.

The router is mounted at '/user', so all routes inside it are prefixed with '/user'. The route '/profile' inside the router becomes '/user/profile' in the app. Requesting '/profile' does not match any route, causing 404.

❓ state_output

advanced

What is the output of nested namespaces with middleware?

Consider this Express app:

const express = require('express');
const app = express();

const apiRouter = express.Router();
const v1Router = express.Router();

v1Router.use((req, res, next) => {
  req.version = 'v1';
  next();
});

v1Router.get('/data', (req, res) => {
  res.send(`API version: ${req.version}`);
});

apiRouter.use('/v1', v1Router);
app.use('/api', apiRouter);

app.listen(3000);

What will be the response body when a client requests GET /api/v1/data?

Express

const express = require('express');
const app = express();

const apiRouter = express.Router();
const v1Router = express.Router();

v1Router.use((req, res, next) => {
  req.version = 'v1';
  next();
});

v1Router.get('/data', (req, res) => {
  res.send(`API version: ${req.version}`);
});

apiRouter.use('/v1', v1Router);
app.use('/api', apiRouter);

app.listen(3000);

A 404 Not Found

B API version: undefined

C API version: v1

D 500 Internal Server Error

💡 Hint

Look at how middleware sets req.version before the route handler.

The middleware on v1Router sets req.version = 'v1' before the route handler runs. So when the client requests /api/v1/data, the response is 'API version: v1'.

🧠 Conceptual

expert

Which statement about Express namespaces (routers) is true?

Choose the correct statement about using namespaces (routers) in Express:

A Routers cannot have middleware; middleware must be applied only on the main app instance.

B Routers can be nested and each can have its own middleware and routes, allowing modular route separation.

C Routes defined in routers lose access to the original request object properties.

D Routers automatically merge query parameters from parent routers without extra configuration.

💡 Hint

Think about how routers help organize routes and middleware.

Express routers can be nested and each router can have its own middleware and routes. This allows developers to separate routes into modules or namespaces. Middleware applies normally within routers. Options A, C, and D are incorrect because routers do support middleware, routes keep access to request properties, and query parameters are passed normally but not 'automatically merged' in a special way.