req.headers for HTTP headers in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access HTTP headers in an Express route.

Express

app.get('/info', (req, res) => {
  const headers = req.[1];
  res.send(headers);
});

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

Aquery

Bbody

Cparams

Dheaders

Attempts:

3 left

💡 Hint

Common Mistakes

Using req.body instead of req.headers

Using req.params or req.query which are for URL parts

The req.headers object contains all HTTP headers sent by the client.

2fill in blank

medium

Complete the code to read the 'user-agent' header from the request.

Express

app.get('/agent', (req, res) => {
  const userAgent = req.headers['[1]'];
  res.send(userAgent);
});

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

Acontent-type

Baccept

Cuser-agent

Dauthorization

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'User-Agent' with uppercase letters (headers keys are lowercase)

Using other header names like 'authorization'

The 'user-agent' header tells the server about the client's browser or tool.

3fill in blank

hard

Fix the error in accessing the 'content-type' header from the request.

Express

app.post('/data', (req, res) => {
  const contentType = req.[1]['content-type'];
  res.send(contentType);
});

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

Aparams

Bheaders

Cbody

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get headers from req.body or req.params

Using wrong property names

The 'content-type' header is inside req.headers, not in body, params, or query.

4fill in blank

hard

Fill both blanks to check if the 'authorization' header exists and send a response.

Express

app.get('/auth', (req, res) => {
  if (req.[1]['[2]']) {
    res.send('Authorized');
  } else {
    res.status(401).send('Unauthorized');
  }
});

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

Aheaders

Bauthorization

Cbody

Dparams

Attempts:

3 left

💡 Hint

Common Mistakes

Checking req.body or req.params instead of req.headers

Using wrong header name spelling

Check req.headers['authorization'] to see if the client sent an authorization token.

5fill in blank

hard

Fill all three blanks to create a middleware that logs the 'host' header and calls next().

Express

function logHost(req, res, [1]) {
  console.log('Host:', req.[2]['[3]']);
  [1]();
}

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

Anext

Bheaders

Chost

Dres

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter name instead of next

Accessing headers from wrong object

Forgetting to call next()

Middleware functions get next as the third argument. Use req.headers['host'] to get the host header, then call next() to continue.

Practice

1. What does req.headers represent in an Express app?

easy

A. A function to send headers to the client

B. An object containing all HTTP headers sent by the client

C. A string with the URL path of the request

D. A number representing the HTTP status code

Solution

1. Step 1: Understand the role of req.headers

   req.headers holds all headers sent by the client in the HTTP request.

2. Step 2: Identify what req.headers contains

   It is an object with keys as header names (lowercase) and values as header values.

3. Final Answer:

   An object containing all HTTP headers sent by the client -> Option B

4. Quick Check:

   req.headers = client headers [OK]

Hint: Remember: req.headers holds client headers as an object [OK]

Common Mistakes:

• Thinking req.headers is a function
• Confusing headers with URL or status code
• Expecting headers keys to be uppercase

2. Which of the following is the correct way to access the 'content-type' header from req.headers?

easy

A. req.headers.Content-Type

B. req.headers['Content-Type']

C. req.headers.contentType

D. req.headers['content-type']

Solution

1. Step 1: Recall header key casing in req.headers

   Headers keys are always lowercase in req.headers.

2. Step 2: Choose the correct syntax to access the header

   Use bracket notation with lowercase key: req.headers['content-type'].

3. Final Answer:

   req.headers['content-type'] -> Option D

4. Quick Check:

   Headers keys are lowercase strings [OK]

Hint: Use lowercase keys with bracket notation for headers [OK]

Common Mistakes:

• Using camelCase or uppercase keys
• Using dot notation with hyphenated keys
• Assuming headers keys keep original case

3. Given this Express code snippet:

app.get('/', (req, res) => {
  const userAgent = req.headers['user-agent'];
  res.send(userAgent);
});

What will the server send back to the client?

medium

A. An error because 'user-agent' is not a valid header

B. The server's operating system name

C. The client's browser user agent string

D. An empty string

Solution

1. Step 1: Identify what req.headers['user-agent'] contains

   This header holds the client's browser and system info string.

2. Step 2: Understand the response sent

   The server sends back this string as the response body using res.send().

3. Final Answer:

   The client's browser user agent string -> Option C

4. Quick Check:

   req.headers['user-agent'] = client info [OK]

Hint: User-Agent header shows client browser info [OK]

Common Mistakes:

• Thinking it returns server info
• Assuming 'user-agent' header is invalid
• Expecting an error or empty response

4. What is wrong with this code snippet?

app.get('/data', (req, res) => {
  const auth = req.headers.Authorization;
  if (!auth) {
    res.status(401).send('Unauthorized');
  } else {
    res.send('Access granted');
  }
});

medium

A. Header keys in req.headers are lowercase, so 'Authorization' should be 'authorization'

B. Header keys in req.headers are case-sensitive and 'Authorization' is correct

C. You cannot access headers directly from req.headers

D. res.status() cannot be chained with res.send()

Solution

1. Step 1: Check header key casing in req.headers

   All header keys are lowercase, so 'Authorization' is incorrect.

2. Step 2: Correct the header key usage

   Use req.headers.authorization to access the Authorization header properly.

3. Final Answer:

   Header keys in req.headers are lowercase, so 'Authorization' should be 'authorization' -> Option A

4. Quick Check:

   Headers keys are lowercase strings [OK]

Hint: Always use lowercase keys for req.headers access [OK]

Common Mistakes:

• Using uppercase or camelCase header keys
• Thinking headers are case-sensitive as sent
• Believing res.status() and res.send() can't chain

5. You want to check if a client sent a custom header named 'X-Client-Id' and respond with 'Client ID: <id>'. Which code correctly handles this in Express?

hard

A. const clientId = req.headers['x-client-id']; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID');

B. const clientId = req.headers.xClientId; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID');

C. const clientId = req.headers['X-Client-Id']; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID');

D. const clientId = req.headers.get('X-Client-Id'); if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID');

Solution

1. Step 1: Understand header key casing in req.headers

   Headers keys are lowercase, so use req.headers['x-client-id'].

2. Step 2: Verify the correct way to access custom headers

   const clientId = req.headers['x-client-id']; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID'); uses lowercase key and bracket notation correctly to get the header value.

3. Step 3: Check other options

   const clientId = req.headers['X-Client-Id']; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID'); uses uppercase keys (wrong), B uses camelCase (wrong), D uses req.headers.get('X-Client-Id') which doesn't exist on req.headers.

4. Final Answer:

   const clientId = req.headers['x-client-id']; if(clientId) res.send(`Client ID: ${clientId}`); else res.send('No Client ID'); -> Option A

5. Quick Check:

   Headers keys lowercase in req.headers [OK]

Hint: Custom headers keys are lowercase in req.headers [OK]

Common Mistakes:

• Using uppercase or camelCase keys
• Confusing req.headers with req.get()
• Accessing headers with dot notation for hyphenated names