res.set for response headers in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the Content-Type header to 'application/json'.

Express

res.[1]('Content-Type', 'application/json');

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

Asend

Bset

Cget

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.send instead of res.set, which sends the response body instead of setting headers.

Using res.get, which retrieves headers but does not set them.

The res.set method sets HTTP headers on the response. Here, it sets the 'Content-Type' header.

2fill in blank

medium

Complete the code to set multiple headers at once using an object.

Express

res.[1]({ 'Cache-Control': 'no-cache', 'X-Powered-By': 'Express' });

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

Asend

BwriteHead

Cheader

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.send which sends the response body, not headers.

Using res.writeHead which is a Node.js method but not typical in Express.

The res.set method can accept an object to set multiple headers at once.

3fill in blank

hard

Fix the error in setting a header by completing the method name correctly.

Express

res.[1]('Authorization', 'Bearer token123');

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

Aset

BsetHeader

Cheader

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.setHeader which is not the Express method.

Using res.write which is for writing response body.

In Express, the correct method to set headers is res.set. setHeader is a Node.js method but not used directly on Express response objects.

4fill in blank

hard

Fill both blanks to set the 'Content-Language' header to 'en-US'.

Express

res.[1]('[2]', 'en-US');

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

Aset

Bsend

CContent-Language

DContent-Type

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Content-Type' instead of 'Content-Language'.

Using res.send instead of res.set.

The res.set method sets headers. The header name here is 'Content-Language'.

5fill in blank

hard

Fill all three blanks to set headers 'X-Frame-Options' to 'DENY', 'Strict-Transport-Security' to 'max-age=31536000', and 'Referrer-Policy' to 'no-referrer'.

Express

res.[1]({ [2]: 'DENY', [3]: 'max-age=31536000', 'Referrer-Policy': 'no-referrer' });

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

Aset

BX-Frame-Options

CStrict-Transport-Security

DContent-Security-Policy

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names like res.send or res.write.

Using incorrect header names or misspelling them.

Use res.set to set multiple headers at once. The keys are the header names exactly as required.

Practice

1. What does res.set do in an Express response?

easy

A. It sets or updates HTTP headers before sending the response.

B. It sends the response body to the client.

C. It closes the server connection immediately.

D. It logs request details to the console.

Solution

1. Step 1: Understand the purpose of res.set

   res.set is used to add or modify HTTP headers in the response before sending it.

2. Step 2: Differentiate from other response methods

   Sending the body is done by res.send, not res.set. Logging or closing connections are unrelated.

3. Final Answer:

   It sets or updates HTTP headers before sending the response. -> Option A

4. Quick Check:

   res.set sets headers [OK]

Hint: Remember: res.set changes headers, not body or connection [OK]

Common Mistakes:

• Confusing res.set with res.send
• Thinking res.set sends the response
• Assuming res.set closes the connection

2. Which of the following is the correct syntax to set a single header using res.set?

easy

A. res.set('Content-Type', application/json);

B. res.set('Content-Type', 'application/json');

C. res.set({Content-Type: 'application/json'});

D. res.set('Content-Type' => 'application/json');

Solution

1. Step 1: Recall correct method signature

   The correct syntax for setting one header is res.set(name, value) where both are strings.

2. Step 2: Check each option

   res.set('Content-Type', 'application/json'); uses correct syntax with two string arguments. res.set('Content-Type' => 'application/json'); uses invalid arrow syntax. res.set({Content-Type: 'application/json'}); uses invalid object syntax - unquoted key Content-Type (hyphen requires quotes). res.set('Content-Type', application/json); misses quotes around value.

3. Final Answer:

   res.set('Content-Type', 'application/json'); -> Option B

4. Quick Check:

   Two string args for single header [OK]

Hint: Use two strings for single header: name and value [OK]

Common Mistakes:

• Using arrow => instead of comma
• Passing unquoted values
• Confusing object syntax for single header

3. What will be the value of the Content-Type header after this code runs?

res.set({
  'Content-Type': 'text/html',
  'Cache-Control': 'no-cache'
});
res.set('Content-Type', 'application/json');

medium

A. Undefined (header not set)

B. 'text/html'

C. 'no-cache'

D. 'application/json'

Solution

1. Step 1: Understand header setting order

   First, Content-Type is set to 'text/html' via object. Then it is overwritten by res.set('Content-Type', 'application/json').

2. Step 2: Determine final header value

   The last set value for Content-Type is 'application/json', so that is the final header value.

3. Final Answer:

   'application/json' -> Option D

4. Quick Check:

   Last header set wins [OK]

Hint: Later res.set calls overwrite previous headers [OK]

Common Mistakes:

• Assuming first set value stays
• Confusing other headers with Content-Type
• Thinking headers merge values

4. Identify the error in this Express code snippet:

app.get('/data', (req, res) => {
  res.send('Hello');
  res.set('X-Custom-Header', '123');
});

medium

A. Headers must be set before sending the response body.

B. res.set cannot set custom headers.

C. res.send should be called twice to set headers.

D. No error; code works fine.

Solution

1. Step 1: Check order of res.set and res.send

   Headers must be set before calling res.send because sending the body finalizes the response.

2. Step 2: Identify the mistake

   Here, res.send is called first, then res.set, which is too late to add headers.

3. Final Answer:

   Headers must be set before sending the response body. -> Option A

4. Quick Check:

   Set headers before send [OK]

Hint: Always set headers before sending response body [OK]

Common Mistakes:

• Setting headers after res.send
• Thinking res.set can't set custom headers
• Calling res.send multiple times

5. You want to set multiple headers including Content-Type and Cache-Control in one call, but only if a condition is true. Which code correctly uses res.set with condition?

hard

A. res.set({'Content-Type': isJson ? 'application/json' : 'text/html'}); res.set('Cache-Control', 'no-store');

B. res.set('Content-Type', isJson ? 'application/json' : 'text/html', 'Cache-Control', 'no-store');

C. if (isJson) res.set({'Content-Type': 'application/json', 'Cache-Control': 'no-store'});

D. res.set('Content-Type', 'application/json' && 'Cache-Control', 'no-store');

Solution

1. Step 1: Understand how to set multiple headers conditionally

   Using an object with res.set allows setting many headers at once. Wrapping in an if statement applies condition.

2. Step 2: Evaluate each option

   if (isJson) res.set({'Content-Type': 'application/json', 'Cache-Control': 'no-store'}); correctly uses an if condition and sets multiple headers in one object. res.set('Content-Type', isJson ? 'application/json' : 'text/html', 'Cache-Control', 'no-store'); has invalid syntax with multiple pairs in one call. res.set({'Content-Type': isJson ? 'application/json' : 'text/html'}); res.set('Cache-Control', 'no-store'); splits headers into two calls but is valid; however, question asks for one call. res.set('Content-Type', 'application/json' && 'Cache-Control', 'no-store'); uses invalid logical operator in arguments.

3. Final Answer:

   if (isJson) res.set({'Content-Type': 'application/json', 'Cache-Control': 'no-store'}); -> Option C

4. Quick Check:

   if + res.set(object) for conditional multiple [OK]

Hint: Use object syntax inside if to set multiple headers [OK]

Common Mistakes:

• Passing multiple header pairs as separate arguments
• Using logical operators inside res.set arguments
• Setting headers outside condition