req.cookies with cookie-parser in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the cookie-parser middleware.

Express

const express = require('express');
const cookieParser = require([1]);

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

A'cors'

B'express'

C'body-parser'

D'cookie-parser'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'express' instead of 'cookie-parser' in require.

Confusing cookie-parser with body-parser.

The cookie-parser package is imported by requiring 'cookie-parser'.

2fill in blank

medium

Complete the code to use cookie-parser middleware in the Express app.

Express

const app = express();
app.use([1]());

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

Aexpress.json

BcookieParser

Cexpress.urlencoded

Dcors

Attempts:

3 left

💡 Hint

Common Mistakes

Using express.json() instead of cookieParser().

Forgetting to call the function with parentheses.

To enable cookie parsing, you use cookieParser() as middleware.

3fill in blank

hard

Fix the error in accessing cookies from the request object.

Express

app.get('/', (req, res) => {
  const userCookie = req.[1].user;
  res.send(`User cookie: ${userCookie}`);
});

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

Acookies

Bcookie

Cheaders

Dparams

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.cookie instead of req.cookies.

Trying to access cookies from req.headers directly.

Cookies parsed by cookie-parser are available on req.cookies.

4fill in blank

hard

Fill both blanks to set up cookie-parser with a secret and access signed cookies.

Express

const cookieParser = require('cookie-parser');
app.use(cookieParser([1]));

app.get('/signed', (req, res) => {
  const signedCookie = req.[2].token;
  res.send(`Signed cookie: ${signedCookie}`);
});

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

A'mySecret'

Bcookies

CsignedCookies

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing null or no secret when signed cookies are needed.

Accessing signed cookies from req.cookies instead of req.signedCookies.

Passing a secret string to cookie-parser enables signed cookies, which are accessed via req.signedCookies.

5fill in blank

hard

Fill all three blanks to create a route that reads a cookie and sets a new cookie.

Express

app.get('/cookie', (req, res) => {
  const oldValue = req.[1].sessionId;
  res.cookie([2], 'abc123', { httpOnly: true });
  res.send(`Old session: ${oldValue}`);
});

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

Acookies

B'sessionId'

DsignedCookies

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.signedCookies when the cookie is not signed.

Forgetting to put cookie name in quotes when setting cookie.

Cookies are read from req.cookies. To set a cookie, use res.cookie('cookieName', value). Here, the cookie name is 'sessionId'.

Practice

1. What does req.cookies represent in an Express app when using cookie-parser middleware?

easy

A. A function to set cookies on the response

B. An object containing cookies sent by the browser

C. A string of all cookies concatenated

D. An array of cookie names only

Solution

1. Step 1: Understand the role of cookie-parser

   The cookie-parser middleware parses cookies from the HTTP request headers.

2. Step 2: Identify what req.cookies holds

   After parsing, req.cookies is an object where each cookie name is a key and its value is the cookie's value.

3. Final Answer:

   An object containing cookies sent by the browser -> Option B

4. Quick Check:

   req.cookies = object of cookies [OK]

Hint: Remember: req.cookies is an object, not a string or function [OK]

Common Mistakes:

• Thinking req.cookies is a function
• Expecting req.cookies to be a string
• Confusing req.cookies with response cookies

2. Which of the following is the correct way to use cookie-parser middleware in an Express app?

easy

A. app.use(cookieParser);

B. app.cookieParser();

C. app.use(cookieParser());

D. ;)(resraPeikooc.ppa

Solution

1. Step 1: Recall middleware usage in Express

   Middleware functions are added using app.use() and must be called as functions if they return middleware.

2. Step 2: Apply this to cookie-parser

   The correct syntax is app.use(cookieParser()); to invoke the function and add the middleware.

3. Final Answer:

   app.use(cookieParser()); -> Option C

4. Quick Check:

   Middleware added with app.use(cookieParser()) [OK]

Hint: Use parentheses to call middleware function inside app.use [OK]

Common Mistakes:

• Forgetting parentheses after cookieParser
• Calling cookieParser as a method on app
• Passing cookieParser without calling it

3. Given this Express route with cookie-parser middleware, what will be the output if the browser sends a cookie named user with value alice?

app.get('/profile', (req, res) => {
  res.send(`User: ${req.cookies.user}`);
});

medium

A. User: [object Object]

B. User: undefined

C. Error: req.cookies is not defined

D. User: alice

Solution

1. Step 1: Check if cookie-parser is used

   Assuming cookie-parser middleware is active, req.cookies contains parsed cookies.

2. Step 2: Access the user cookie value

   The code accesses req.cookies.user, which equals 'alice' from the browser cookie.

3. Final Answer:

   User: alice -> Option D

4. Quick Check:

   Cookie value accessed correctly = User: alice [OK]

Hint: Access cookie by name on req.cookies object [OK]

Common Mistakes:

• Not using cookie-parser so req.cookies is undefined
• Trying to access cookies as a string
• Assuming cookie names are case-insensitive

4. What is wrong with this Express code snippet if req.cookies is always undefined?

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();

app.get('/', (req, res) => {
  res.send(req.cookies);
});

app.use(cookieParser());

medium

A. cookie-parser middleware is added after the route, so req.cookies is undefined

B. cookie-parser is not imported correctly

C. The route handler should use res.cookies instead

D. Express does not support cookies natively

Solution

1. Step 1: Check middleware order

   Middleware must be added before routes to affect req objects in those routes.

2. Step 2: Identify the problem in code

   Here, app.use(cookieParser()) is after the route, so req.cookies is not set when the route runs.

3. Final Answer:

   cookie-parser middleware is added after the route, so req.cookies is undefined -> Option A

4. Quick Check:

   Middleware order matters = cookie-parser middleware is added after the route, so req.cookies is undefined [OK]

Hint: Add middleware before routes to access req.cookies [OK]

Common Mistakes:

• Placing middleware after routes
• Confusing req.cookies with res.cookies
• Not calling cookieParser as a function

5. You want to create an Express route that reads a cookie named theme and sends back 'Dark mode' if its value is 'dark', otherwise 'Light mode'. Which code correctly implements this using req.cookies with cookie-parser?

hard

A. app.get('/mode', (req, res) => {
if (req.cookies.theme === 'dark') res.send('Dark mode');
else res.send('Light mode');
});

B. app.get('/mode', (req, res) => {
if (req.cookies['theme'] = 'dark') res.send('Dark mode');
else res.send('Light mode');
});

C. app.get('/mode', (req, res) => {
if (req.cookies.theme == dark) res.send('Dark mode');
else res.send('Light mode');
});

D. app.get('/mode', (req, res) => {
if (req.cookies.theme === dark) res.send('Dark mode');
else res.send('Light mode');
});

Solution

1. Step 1: Check cookie access and comparison

   Use strict equality === to compare req.cookies.theme to the string 'dark'.

2. Step 2: Identify correct syntax

   app.get('/mode', (req, res) => { if (req.cookies.theme === 'dark') res.send('Dark mode'); else res.send('Light mode'); }); uses === and string 'dark' correctly. app.get('/mode', (req, res) => { if (req.cookies['theme'] = 'dark') res.send('Dark mode'); else res.send('Light mode'); }); uses assignment = instead of comparison. app.get('/mode', (req, res) => { if (req.cookies.theme == dark) res.send('Dark mode'); else res.send('Light mode'); }); uses loose equality == with unquoted dark. app.get('/mode', (req, res) => { if (req.cookies.theme === dark) res.send('Dark mode'); else res.send('Light mode'); }); uses undefined variable dark without quotes.

3. Final Answer:

   The code using strict equality req.cookies.theme === 'dark' -> Option A

4. Quick Check:

   Use === 'dark' to compare cookie value [OK]

Hint: Use === and quotes for string comparison with cookie values [OK]

Common Mistakes:

• Using = instead of === for comparison
• Not quoting string literals
• Using loose equality == instead of ===