Virtual path prefixes in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Express

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

app.use([1], router);

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

A'/api'

B'api'

C'/router'

D'/'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'api' without the leading slash

Using '/' which mounts at root

The virtual path prefix must start with a slash, so '/api' is correct.

2fill in blank

medium

Complete the code to define a GET route on the router for '/users'.

Express

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

router.[1]('/users', (req, res) => {
  res.send('User list');
});

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

Adelete

Bpost

Cput

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'post' instead of 'get'

Using 'put' or 'delete' for fetching data

The GET method is used to define a route that responds to GET requests.

3fill in blank

hard

Fix the error in mounting the router so it uses the virtual path prefix '/api'.

Express

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

app.use([1], router);

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

A'/api'

Brouter

C'api'

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of arguments

Using 'api' without slash

The first argument to app.use should be the path prefix string, followed by the router.

4fill in blank

hard

Fill both blanks to create a router mounted on '/admin' that responds to GET requests at '/dashboard'.

Express

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

router.[1]('/dashboard', (req, res) => {
  res.send('Admin Dashboard');
});

app.use([2], router);

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

Aget

Bpost

C'/admin'

D'/dashboard'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'post' instead of 'get'

Mounting on wrong path like '/dashboard'

Use 'get' to define the GET route and '/admin' as the virtual path prefix.

5fill in blank

hard

Fill all three blanks to create a router mounted on '/shop' with a POST route at '/order' that sends 'Order received'.

Express

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

router.[1]([2], (req, res) => {
  res.send('Order received');
});

app.use([3], router);

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

Apost

B'/order'

C'/shop'

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'post'

Wrong route or mount paths

Use 'post' for the POST route, '/order' as the route path, and mount the router on '/shop'.

Practice

1. What is the main purpose of using a virtual path prefix in Express with app.use('/prefix', router)?

easy

A. To handle errors globally in the app

B. To create a new Express app instance

C. To serve static files from a directory

D. To group routes under a common URL path for better organization

Solution

1. Step 1: Understand what app.use('/prefix', router) does

   This syntax mounts a router or middleware under the URL path '/prefix'.

2. Step 2: Identify the purpose of grouping routes

   Grouping routes under a common prefix helps organize and maintain the app's URL structure.

3. Final Answer:

   To group routes under a common URL path for better organization -> Option D

4. Quick Check:

   Virtual path prefix = route grouping [OK]

Hint: Virtual path prefixes group routes under one URL path [OK]

Common Mistakes:

• Thinking it creates a new app instance
• Confusing with static file serving
• Assuming it handles errors

2. Which of the following is the correct syntax to mount a router on the virtual path prefix '/api' in Express?

easy

A. app.route('/api', router);

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

C. app.mount('/api', router);

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

Solution

1. Step 1: Recall Express method to mount middleware or routers

   Express uses app.use(path, middleware) to mount routers or middleware.

2. Step 2: Check each option's method name

   Only app.use is the correct method; others like app.route, app.mount, and app.router are invalid or incorrect here.

3. Final Answer:

   app.use('/api', router); -> Option B

4. Quick Check:

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

Hint: Use app.use to mount routers on paths [OK]

Common Mistakes:

• Using app.route instead of app.use
• Trying non-existent methods like app.mount
• Confusing router mounting with route definitions

3. Given the code below, what URL path will respond with 'Hello from admin'?

const express = require('express');
const app = express();
const adminRouter = express.Router();
adminRouter.get('/', (req, res) => res.send('Hello from admin'));
app.use('/admin', adminRouter);
app.listen(3000);

medium

A. http://localhost:3000/

B. http://localhost:3000/admin

C. http://localhost:3000/admin/

D. http://localhost:3000/admin/home

Solution

1. Step 1: Understand the router path and mounting prefix

   The router handles GET requests at '/' and is mounted at '/admin'.

2. Step 2: Combine prefix and router path

   The full path is '/admin' + '/' = '/admin/'.

3. Step 3: Understand URL normalization

   URLs with or without trailing slash for this route behave the same in Express, so both '/admin' and '/admin/' respond with 'Hello from admin'.

4. Final Answer:

   http://localhost:3000/admin/ and http://localhost:3000/admin -> Option C

5. Quick Check:

   Router '/' + mount '/admin' = '/admin/' and '/admin' [OK]

Hint: Combine mount path and router path for full URL; trailing slash optional [OK]

Common Mistakes:

• Ignoring trailing slash in URL
• Assuming root '/' responds without prefix
• Confusing '/admin' and '/admin/home'

4. Identify the error in this Express code snippet that tries to mount a router with a virtual path prefix:

const express = require('express');
const app = express();
const userRouter = express.Router();
userRouter.get('/profile', (req, res) => res.send('User Profile'));
app.use(userRouter, '/user');
app.listen(3000);

medium

A. The order of arguments in app.use is incorrect

B. The router path '/profile' is invalid

C. Missing app.listen call

D. Router should be created with express() not express.Router()

Solution

1. Step 1: Check the app.use argument order

   Correct syntax is app.use(path, router), but here it is reversed.

2. Step 2: Identify the correct argument order

   It should be app.use('/user', userRouter) to mount the router at '/user'.

3. Final Answer:

   The order of arguments in app.use is incorrect -> Option A

4. Quick Check:

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

Hint: app.use(path, router) not app.use(router, path) [OK]

Common Mistakes:

• Swapping router and path arguments
• Thinking router path is invalid
• Forgetting to call app.listen

5. You want to create an Express app with two routers: adminRouter mounted at '/admin' and userRouter mounted at '/user'. Both routers have a route for '/' that sends different greetings. Which code correctly sets this up so visiting '/admin' and '/user' shows the correct messages?

hard

A. app.use('/admin', adminRouter);
app.use('/user', userRouter);

B. app.use(adminRouter, '/admin');
app.use(userRouter, '/user');

C. app.route('/admin', adminRouter);
app.route('/user', userRouter);

D. app.get('/admin', adminRouter);
app.get('/user', userRouter);

Solution

1. Step 1: Recall correct syntax for mounting routers with prefixes

   Use app.use(path, router) to mount routers at virtual path prefixes.

2. Step 2: Evaluate the options

   The correct code uses app.use('/admin', adminRouter); and app.use('/user', userRouter);. Distractors use invalid methods like app.route() or app.get() with routers, or reverse the path and router order in app.use().

3. Final Answer:

   app.use('/admin', adminRouter); app.use('/user', userRouter); -> Option A

4. Quick Check:

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

Hint: Mount routers with app.use(path, router) for multiple prefixes [OK]

Common Mistakes:

• Swapping router and path in app.use
• Using app.route or app.get to mount routers
• Not mounting routers at all