HTTP caching headers in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of HTTP caching headers?

HTTP caching headers tell browsers and servers how to store and reuse web resources to make loading faster and reduce network traffic.

intermediate

Explain the difference between Cache-Control: no-cache and Cache-Control: no-store.

no-cache means the browser must check with the server before using cached data. no-store means the browser should never save the response at all.

intermediate

What does the ETag header do in HTTP caching?

The ETag is a unique identifier for a resource version. Browsers send it back to the server to check if the resource changed, so they can avoid downloading it again if unchanged.

beginner

How does the Expires header work?

The Expires header tells the browser a specific date and time after which the cached resource is considered stale and must be fetched again.

intermediate

What is the role of Last-Modified header in caching?

The Last-Modified header shows when the resource was last changed. Browsers use it to ask the server if the resource has changed since that date to decide if they need to download it again.

Which HTTP header tells the browser to always check with the server before using cached content?

A ETag

B Cache-Control: no-cache

C Expires

D Cache-Control: no-store

Cache-Control: no-cache means the browser must revalidate with the server before using cached content.

What does the ETag header help with?

A Identifying resource versions for validation

B Setting cache expiration date

C Preventing caching entirely

D Specifying content type

ETag is a unique tag to identify resource versions and help browsers check if content changed.

If you want to prevent any caching of a response, which header should you use?

A Expires: 0

B Cache-Control: no-cache

C Cache-Control: no-store

D Last-Modified

Cache-Control: no-store tells browsers not to save the response at all.

Which header specifies a date/time after which cached content is stale?

A Last-Modified

B Cache-Control

C ETag

D Expires

Expires sets a specific expiration date/time for cached content.

How does the Last-Modified header help caching?

A It tells the browser when the resource was last changed

B It disables caching

C It sets the cache duration

D It identifies the resource version

Last-Modified shows when the resource last changed, helping browsers decide if they need to reload it.

Describe how HTTP caching headers improve website performance and reduce server load.

Think about how your browser can save time by not downloading the same files again.

Explain the difference between Cache-Control: no-cache and Cache-Control: no-store headers.

One lets you keep data but checks before use; the other never saves it.

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