req.cookies with cookie-parser in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does req.cookies contain after using cookie-parser?

Consider an Express app using cookie-parser middleware. A client sends a request with the header Cookie: user=alice; theme=dark. What will req.cookies contain inside a route handler?

Express

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser());
app.get('/', (req, res) => {
  res.json(req.cookies);
});

A {"user": "alice", "theme": "dark"}

B ["user=alice", "theme=dark"]

C undefined

D "user=alice; theme=dark"

💡 Hint

Think about how cookie-parser parses the cookie header into an object.

The cookie-parser middleware parses the cookie header string into an object where each cookie name is a key and its value is the value. So req.cookies is an object like { user: 'alice', theme: 'dark' }.

📝 Syntax

intermediate

Which code correctly uses cookie-parser to access cookies?

Which of the following Express app snippets correctly sets up cookie-parser and accesses a cookie named sessionId?

A

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser);
app.get('/', (req, res) => {
  res.send(req.cookies.sessionId);
});

B

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.get('/', (req, res) => {
  res.send(req.cookies.sessionId);
});
app.use(cookieParser());

C

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser());
app.get('/', (req, res) => {
  res.send(req.cookies.sessionId);
});

D

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser());
app.get('/', (req, res) => {
  res.send(req.cookie.sessionId);
});

💡 Hint

Remember to call cookieParser() as a function and use req.cookies (plural).

Option C correctly calls cookieParser() middleware before routes and accesses req.cookies.sessionId. Option C applies middleware after routes, so cookies won't be parsed. Option C passes the middleware function without calling it. Option C uses req.cookie instead of req.cookies.

🔧 Debug

advanced

Why does req.cookies remain empty despite sending cookies?

An Express app uses cookie-parser middleware. The client sends cookies, but req.cookies is always empty. What is the most likely cause?

Express

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.get('/', (req, res) => {
  res.json(req.cookies);
});
app.use(cookieParser());

A The client did not send any cookies in the request headers.

B The middleware <code>cookie-parser</code> is used after the route, so cookies are not parsed before the route runs.

C The <code>cookie-parser</code> middleware is missing the secret key argument.

D The <code>req.cookies</code> property is deprecated and replaced by <code>req.signedCookies</code>.

💡 Hint

Middleware order matters in Express.

Middleware must be registered before routes to affect them. Here, cookie-parser is registered after the route, so req.cookies is empty inside the route handler.

❓ state_output

advanced

What is the value of req.signedCookies after using cookie-parser('secret')?

Given the Express app below, what will req.signedCookies contain if the client sends a cookie token=abc123 signed with the secret secret?

Express

const express = require('express');
const cookieParser = require('cookie-parser');
const app = express();
app.use(cookieParser('secret'));
app.get('/', (req, res) => {
  res.json({
    cookies: req.cookies,
    signedCookies: req.signedCookies
  });
});

A undefined

B {}

C null

D {"token": "abc123"}

💡 Hint

Signed cookies are verified and available in req.signedCookies.

When cookie-parser is initialized with a secret, it verifies signed cookies. If the signature matches, the cookie appears in req.signedCookies. So req.signedCookies contains the verified cookie { token: 'abc123' }.

🧠 Conceptual

expert

Which statement about cookie-parser and req.cookies is TRUE?

Choose the correct statement about how cookie-parser works with req.cookies in Express.

A <code>cookie-parser</code> parses the <code>Cookie</code> header and populates <code>req.cookies</code> as an object with cookie names and values.

B <code>req.cookies</code> is automatically available in Express without any middleware.

C <code>cookie-parser</code> encrypts cookies before sending them to the client.

D <code>req.cookies</code> contains only signed cookies when <code>cookie-parser</code> is used with a secret.

💡 Hint

Think about what cookie-parser does and what req.cookies holds.

cookie-parser reads the Cookie header and creates an object req.cookies with cookie names and values. It does not encrypt cookies; encryption is done elsewhere. req.cookies is not available without middleware. Signed cookies appear in req.signedCookies, not req.cookies.