On-demand revalidation in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is on-demand revalidation in Next.js?

On-demand revalidation lets you update a static page after it's built, without rebuilding the whole site. You ask Next.js to refresh the page data when something changes.

beginner

Which Next.js function is used to trigger on-demand revalidation?

You use the res.revalidate(path) method inside an API route to tell Next.js to update the static page at the given path.

intermediate

Why use on-demand revalidation instead of rebuilding the whole site?

It saves time and resources by updating only the changed pages, so your site stays fast and fresh without full rebuilds.

beginner

What is a common use case for on-demand revalidation?

When content changes in a CMS or database, you can call on-demand revalidation to update the affected pages immediately.

intermediate

How do you secure an API route that triggers on-demand revalidation?

You add a secret token check in the API route to allow only authorized requests to trigger revalidation.

What does res.revalidate('/path') do in Next.js?

A Disables static generation for '/path'

B Deletes the static page at '/path'

C Triggers a rebuild of the entire site

D Updates the static page at '/path' with fresh data

The res.revalidate('/path') method tells Next.js to regenerate the static page at '/path' with updated data.

Where do you typically call on-demand revalidation in Next.js?

A Inside an API route handler

B Inside getStaticProps

C Inside the _app.js file

D Inside the page component's render method

On-demand revalidation is triggered inside an API route handler where you can call res.revalidate().

Which of these is NOT a benefit of on-demand revalidation?

A Faster updates for changed pages

B Full site rebuild on every content change

C Reduced server load compared to full rebuilds

D Better user experience with fresh content

On-demand revalidation avoids full site rebuilds, so option C is not a benefit.

How can you protect your on-demand revalidation API route?

A By using a secret token check

B By disabling API routes

C By calling revalidate only in getStaticProps

D By using client-side JavaScript only

Adding a secret token check ensures only authorized requests can trigger revalidation.

When is on-demand revalidation most useful?

A When you want to rebuild the entire site daily

B When you want to disable static generation

C When content changes frequently and you want fast updates

D When you never update your site content

On-demand revalidation is great for fast updates when content changes often.

Explain how on-demand revalidation works in Next.js and why it is useful.

Think about how you can refresh a page after it is built without rebuilding the whole site.

Describe how to secure an API route that triggers on-demand revalidation in Next.js.

Consider how to prevent unauthorized users from forcing page updates.

Practice

1. What is the main purpose of on-demand revalidation in Next.js?

easy

A. To disable static site generation completely

B. To rebuild the whole site every time a user visits

C. To update specific static pages instantly without rebuilding the entire site

D. To cache pages permanently without updates

Solution

1. Step 1: Understand static site generation

   Static pages are pre-built and served fast but can become outdated.

2. Step 2: Role of on-demand revalidation

   It updates only specific pages instantly without rebuilding the whole site, keeping content fresh.

3. Final Answer:

   To update specific static pages instantly without rebuilding the entire site -> Option C

4. Quick Check:

   On-demand revalidation = update specific pages fast [OK]

Hint: Remember: on-demand means update only what is needed [OK]

Common Mistakes:

• Thinking it rebuilds the entire site
• Confusing it with disabling static generation
• Assuming pages never update

2. Which Next.js API method is used inside an API route to trigger on-demand revalidation?

easy

A. res.reload(path)

B. res.refresh(path)

C. res.update(path)

D. res.revalidate(path)

Solution

1. Step 1: Identify the method for revalidation

   Next.js provides res.revalidate(path) to trigger revalidation of a page.

2. Step 2: Confirm method usage in API route

   This method is called inside an API route handler to update the static page at the given path.

3. Final Answer:

   res.revalidate(path) -> Option D

4. Quick Check:

   API route uses res.revalidate() to update pages [OK]

Hint: Look for 'revalidate' keyword in the method name [OK]

Common Mistakes:

• Using non-existent methods like res.refresh()
• Confusing with client-side reload methods
• Misspelling the method name

3. Given this API route code snippet, what will happen when a POST request with the correct secret is sent?

export default async function handler(req, res) {
  if (req.method === 'POST' && req.query.secret === process.env.MY_SECRET) {
    await res.revalidate('/blog/post-1')
    return res.json({ revalidated: true })
  }
  return res.status(401).json({ message: 'Invalid token' })
}

medium

A. The page '/blog/post-1' will be revalidated and a success JSON returned

B. The entire site will rebuild and return a success JSON

C. The request will fail with a 401 error regardless of the secret

D. The page '/blog/post-1' will reload on the client side

Solution

1. Step 1: Check request method and secret

   The handler checks if the method is POST and the secret matches the environment variable.

2. Step 2: Call res.revalidate on the specific page

   If conditions pass, it calls res.revalidate('/blog/post-1') to update that page only.

3. Final Answer:

   The page '/blog/post-1' will be revalidated and a success JSON returned -> Option A

4. Quick Check:

   Correct secret + POST triggers revalidation [OK]

Hint: Check method and secret before revalidate call [OK]

Common Mistakes:

• Assuming entire site rebuilds
• Ignoring secret check
• Thinking client reload happens automatically

4. Identify the error in this API route code for on-demand revalidation:

export default async function handler(req, res) {
  if (req.method === 'GET' && req.query.secret === process.env.SECRET) {
    await res.revalidate('/home')
    res.json({ revalidated: true })
  } else {
    res.status(401).json({ message: 'Unauthorized' })
  }
}

medium

A. Missing await before res.json()

B. Not returning after res.json() causing possible errors

C. Using GET method instead of POST for revalidation

D. Incorrect path string in res.revalidate()

Solution

1. Step 1: Check response handling after revalidation

   After calling res.revalidate() and sending JSON, the function should return to avoid continuing execution.

2. Step 2: Identify missing return statement

   The code calls res.json() but does not return, which can cause errors or multiple responses.

3. Final Answer:

   Not returning after res.json() causing possible errors -> Option B

4. Quick Check:

   Always return after sending response [OK]

Hint: Return immediately after sending response [OK]

Common Mistakes:

• Using GET instead of POST (allowed but not recommended)
• Forgetting to return after res.json()
• Assuming res.revalidate() rebuilds entire site

5. You want to revalidate multiple pages on-demand after updating content. Which approach correctly triggers revalidation for '/about' and '/contact' in one API route?

hard

A. await res.revalidate('/about'); await res.revalidate('/contact'); res.json({ revalidated: true })

B. await res.revalidate(['/about', '/contact']); res.json({ revalidated: true })

C. res.revalidate('/about', '/contact'); res.json({ revalidated: true })

D. res.revalidate('/about'); res.revalidate('/contact'); res.json({ revalidated: true })

Solution

1. Step 1: Understand res.revalidate usage

   The res.revalidate() method accepts a single path string and returns a promise.

2. Step 2: Revalidate multiple pages sequentially

   To revalidate multiple pages, call await res.revalidate() separately for each path before sending response.

3. Final Answer:

   await res.revalidate('/about'); await res.revalidate('/contact'); res.json({ revalidated: true }) -> Option A

4. Quick Check:

   Call res.revalidate() separately for each page [OK]

Hint: Call revalidate separately for each page with await [OK]

Common Mistakes:

• Passing array of paths to res.revalidate() (not supported)
• Calling res.revalidate without await causing race conditions
• Calling res.revalidate without returning or sending response