Mounting routers with app.use in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mount the router on the '/api' path.

Express

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

app.[1]('/api', router);

Drag options to blanks, or click blank then click option'

Ause

Bget

Cpost

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using app.get or app.post instead of app.use to mount routers.

Trying to call app.listen instead of mounting the router.

Use app.use to mount a router on a path prefix.

2fill in blank

medium

Complete the code to create a new router instance.

Express

const express = require('express');
const router = express.[1]();

Drag options to blanks, or click blank then click option'

Ause

Brouter

Capp

DRouter

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'router' instead of 'Router'.

Trying to call express.app() or express.use() to create a router.

Use express.Router() to create a new router instance.

3fill in blank

hard

Fix the error in mounting the router on the '/users' path.

Express

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

app.[1]('/users', usersRouter);

Drag options to blanks, or click blank then click option'

Aget

Bpost

Cuse

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using app.get or app.post instead of app.use to mount routers.

Trying to call app.listen instead of mounting the router.

To mount a router on a path, use app.use, not app.get or app.post.

4fill in blank

hard

Fill both blanks to mount a router that handles '/products' routes.

Express

const express = require('express');
const app = express();
const [1] = express.Router();

app.[2]('/products', [1]);

Drag options to blanks, or click blank then click option'

AproductsRouter

Buse

Crouter

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using app.get instead of app.use to mount the router.

Using a generic router name instead of a descriptive one.

Create a router named productsRouter and mount it with app.use on '/products'.

5fill in blank

hard

Fill all three blanks to create and mount a router for '/orders' routes.

Express

const express = require('express');
const app = express();
const [1] = express.[2]();

app.[3]('/orders', [1]);

Drag options to blanks, or click blank then click option'

AordersRouter

BRouter

Cuse

Drouter

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'router' instead of 'Router' when creating the router.

Using app.get or app.post instead of app.use to mount the router.

Create a router named ordersRouter using express.Router() and mount it with app.use on '/orders'.

Practice

1. What is the main purpose of using app.use to mount routers in Express?

easy

A. To automatically generate HTML pages

B. To directly send responses without defining routes

C. To group related routes under a common base path for better organization

D. To replace the Express app with a router

Solution

1. Step 1: Understand what app.use does

   app.use mounts middleware or routers at a specified path, grouping routes.

2. Step 2: Identify the benefit of mounting routers

   Mounting routers organizes routes under a base path, making code cleaner and easier to maintain.

3. Final Answer:

   To group related routes under a common base path for better organization -> Option C

4. Quick Check:

   Mount routers = group routes [OK]

Hint: Mount routers to group routes under one path [OK]

Common Mistakes:

• Thinking app.use replaces the app
• Believing it sends responses directly
• Confusing mounting with automatic page generation

2. Which of the following is the correct syntax to mount a router named userRouter on the path /users using app.use?

easy

A. app.use('/users', userRouter);

B. app.use(userRouter, '/users');

C. app.get('/users', userRouter);

D. app.mount('/users', userRouter);

Solution

1. Step 1: Recall the app.use syntax

   The correct syntax is app.use(path, router) to mount a router at a path.

2. Step 2: Match the correct order and method

   app.use('/users', userRouter); uses app.use('/users', userRouter); which is correct. Others have wrong order or method.

3. Final Answer:

   app.use('/users', userRouter); -> Option A

4. Quick Check:

   app.use(path, router) = correct syntax [OK]

Hint: Remember: app.use(path, router) mounts router [OK]

Common Mistakes:

• Swapping router and path order
• Using app.get instead of app.use
• Using non-existent app.mount method

3. Given the following code, what URL path will respond with 'User list'?

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

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

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

medium

A. /users/

B. /

C. /user/

D. /users/list

Solution

1. Step 1: Understand router path and mounting

   The router defines a GET route at '/' which is relative to where it is mounted.

2. Step 2: Combine mount path and router route

   Since userRouter is mounted at '/users', the full path is '/users/' to reach the route.

3. Final Answer:

   /users/ -> Option A

4. Quick Check:

   Mount path + router route = full URL [OK]

Hint: Router path '/' + mount '/users' = '/users/' [OK]

Common Mistakes:

• Ignoring mount path and using '/' alone
• Confusing '/user/' with '/users/'
• Assuming '/users/list' without route defined

4. What is wrong with this code snippet?

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

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

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

medium

A. Missing app.listen call

B. Router cannot have routes with '/info' path

C. app.use cannot mount routers

D. The arguments to app.use are in the wrong order

Solution

1. Step 1: Check app.use argument order

   The correct order is app.use(path, router), but here it is reversed.

2. Step 2: Identify the error cause

   Passing router first and path second causes Express to treat router as middleware without a path, leading to unexpected behavior.

3. Final Answer:

   The arguments to app.use are in the wrong order -> Option D

4. Quick Check:

   app.use(path, router) order matters [OK]

Hint: app.use(path, router) order is strict [OK]

Common Mistakes:

• Swapping router and path in app.use
• Thinking router paths can't have '/info'
• Ignoring missing app.listen (not related here)

5. You want to mount two routers, adminRouter and userRouter, so that /admin/dashboard and /users/profile work correctly. Which code correctly mounts both routers?

hard

A. app.use(adminRouter, '/admin');\napp.use(userRouter, '/users');

B. app.use('/admin', adminRouter);\napp.use('/users', userRouter);

C. app.use('/admin/dashboard', adminRouter);\napp.use('/users/profile', userRouter);

D. app.get('/admin', adminRouter);\napp.get('/users', userRouter);

Solution

1. Step 1: Understand mounting routers at base paths

   Mount routers at base paths like '/admin' and '/users' so their internal routes append correctly.

2. Step 2: Check each option for correct syntax and paths

   app.use('/admin', adminRouter);\napp.use('/users', userRouter); uses app.use('/admin', adminRouter); and app.use('/users', userRouter);, which is correct. app.use(adminRouter, '/admin');\napp.use(userRouter, '/users'); swaps arguments, C mounts at full paths (not base), D uses app.get which is incorrect for mounting routers.

3. Final Answer:

   app.use('/admin', adminRouter); app.use('/users', userRouter); -> Option B

4. Quick Check:

   Mount routers at base paths with app.use(path, router) [OK]

Hint: Mount routers at base paths with app.use(path, router) [OK]

Common Mistakes:

• Swapping router and path in app.use
• Mounting routers at full nested paths
• Using app.get instead of app.use for routers