HTTP caching headers in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a Cache-Control header that allows caching for 1 hour.

Node.js

res.setHeader('Cache-Control', '[1]');

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

Aprivate, max-age=0

Bno-cache

Cpublic, max-age=3600

Dno-store

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'no-cache' or 'no-store' disables caching.

Forgetting to specify max-age causes no caching duration.

The Cache-Control header with public, max-age=3600 allows caching for 3600 seconds (1 hour).

2fill in blank

medium

Complete the code to set the ETag header with a unique value.

Node.js

res.setHeader('ETag', '[1]');

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

Aetag-12345

B"12345"

Cetag123

D12345

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the ETag value causes header parsing errors.

Using non-unique ETag values defeats caching benefits.

The ETag value should be a quoted string, like "12345", to be valid.

3fill in blank

hard

Fix the error in setting the Expires header to 1 day from now.

Node.js

const expires = new Date(Date.now() + [1]).toUTCString();
res.setHeader('Expires', expires);

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

A86400000

B3600000

C60000

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3600000 sets only 1 hour instead of 1 day.

Using 60000 sets only 1 minute.

86400000 milliseconds equals 1 day (24 hours * 60 minutes * 60 seconds * 1000 ms).

4fill in blank

hard

Fill both blanks to set Cache-Control for private caching and must-revalidate directive.

Node.js

res.setHeader('Cache-Control', '[1], [2]');

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

Aprivate

Bpublic

Cmust-revalidate

Dno-store

Attempts:

3 left

💡 Hint

Common Mistakes

Using public instead of private allows shared caching.

Omitting must-revalidate may cause stale content.

Setting private allows caching only for a single user, and must-revalidate forces revalidation after expiration.

5fill in blank

hard

Fill all three blanks to set Cache-Control with max-age 600 and no-transform directives.

Node.js

res.setHeader('Cache-Control', '[1]=[2], [3]');

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

Amax-age

B600

Cno-store

Dno-transform

Attempts:

3 left

💡 Hint

Common Mistakes

Using no-store with max-age is contradictory but allowed; no-store disables caching.

Forgetting to provide max-age value causes errors.

This sets max-age to 600 seconds and disables transformations on the response.

Practice

1. What does the Cache-Control: max-age=3600 header instruct the browser to do?

easy

A. Cache the response for 3600 seconds before checking for updates

B. Never cache the response

C. Cache the response indefinitely

D. Only cache the response if the user is offline

Solution

1. Step 1: Understand the max-age directive meaning

   The max-age directive tells the browser how many seconds it can keep the cached response before it must revalidate.

2. Step 2: Interpret max-age=3600

   max-age=3600 means the browser should cache the response for 3600 seconds (1 hour) before checking for a new version.

3. Final Answer:

   Cache the response for 3600 seconds before checking for updates -> Option A

4. Quick Check:

   max-age=3600 = Cache 1 hour [OK]

Hint: max-age sets cache time in seconds [OK]

Common Mistakes:

• Confusing max-age with no-cache
• Thinking max-age means no caching
• Assuming max-age caches forever

2. Which of the following is the correct way to set a no-store cache control header in a Node.js HTTP response?

easy

A. res.header('Cache-Control', 'no-store')

B. res.setHeader('Cache-Control', 'no-store')

C. res.set('Cache-Control', 'no-store')

D. res.cacheControl = 'no-store'

Solution

1. Step 1: Recall Node.js HTTP response header syntax

   In Node.js, the method to set headers is res.setHeader(name, value).

2. Step 2: Match the correct method and header

   res.setHeader('Cache-Control', 'no-store') uses res.setHeader('Cache-Control', 'no-store'), which is the correct syntax to set the no-store directive.

3. Final Answer:

   res.setHeader('Cache-Control', 'no-store') -> Option B

4. Quick Check:

   Use res.setHeader() to set headers [OK]

Hint: Use res.setHeader() to set HTTP headers [OK]

Common Mistakes:

• Using incorrect method names like res.set or res.header
• Assigning header as a property instead of using setHeader
• Confusing Express methods with Node.js core methods

3. Consider this Node.js code snippet setting caching headers:

res.setHeader('Cache-Control', 'no-cache, max-age=0');
res.end('Hello');

What will the browser do with this response?

medium

A. Ignore caching and always fetch fresh data

B. Cache the response for 0 seconds and never revalidate

C. Cache the response indefinitely without revalidation

D. Cache the response for 0 seconds and revalidate before each use

Solution

1. Step 1: Understand the meaning of no-cache and max-age=0

   The no-cache directive means the browser must revalidate with the server before using the cached response. max-age=0 means the cached response is immediately stale.

2. Step 2: Combine the effects

   With no-cache and max-age=0, the browser caches the response but must check with the server before each use, effectively caching for 0 seconds without skipping validation.

3. Final Answer:

   Cache the response for 0 seconds and revalidate before each use -> Option D

4. Quick Check:

   no-cache + max-age=0 = revalidate every time [OK]

Hint: no-cache means revalidate before use [OK]

Common Mistakes:

• Thinking no-cache means no caching at all
• Ignoring max-age=0 effect
• Assuming browser ignores these headers

4. You wrote this Node.js code to prevent caching:

res.end('Data');
res.setHeader('Cache-Control', 'no-cache, no-store');

But the browser still caches the response. What is the likely mistake?

medium

A. The 'no-store' directive is misspelled

B. The response status code is missing

C. Headers are set after sending the response body

D. The Cache-Control header should be lowercase

Solution

1. Step 1: Check header setting timing

   Headers must be set before sending the response body. If headers are set after calling res.end(), they won't be sent.

2. Step 2: Confirm header spelling and case

   Cache-Control is case-insensitive and 'no-store' is spelled correctly, so these are not issues.

3. Step 3: Status code is optional for caching headers

   Missing status code does not cause caching issues here.

4. Final Answer:

   Headers are set after sending the response body -> Option C

5. Quick Check:

   Set headers before res.end() [OK]

Hint: Set headers before sending response body [OK]

Common Mistakes:

• Setting headers after res.end()
• Misspelling cache directives
• Assuming header case matters

5. You want to serve a JSON API response that should never be cached by browsers or proxies. Which combination of HTTP caching headers in Node.js ensures this behavior?

hard

A. res.setHeader('Cache-Control', 'no-store, no-cache, must-revalidate')

B. res.setHeader('Cache-Control', 'max-age=3600')

C. res.setHeader('Cache-Control', 'public, max-age=86400')

D. res.setHeader('Cache-Control', 'private, max-age=0')

Solution

1. Step 1: Understand no-store and no-cache directives

   no-store prevents any caching anywhere. no-cache forces revalidation. must-revalidate requires caches to obey freshness rules strictly.

2. Step 2: Analyze each option

   res.setHeader('Cache-Control', 'no-store, no-cache, must-revalidate') combines all directives to prevent caching fully. res.setHeader('Cache-Control', 'max-age=3600') and C allow caching. res.setHeader('Cache-Control', 'private, max-age=0') allows private caching but with max-age=0, which still permits revalidation.

3. Final Answer:

   res.setHeader('Cache-Control', 'no-store, no-cache, must-revalidate') -> Option A

4. Quick Check:

   no-store + no-cache = no caching [OK]

Hint: Use no-store to fully prevent caching [OK]

Common Mistakes:

• Using max-age allowing caching
• Confusing private with no-store
• Omitting must-revalidate for strictness