Revalidation after mutation in NextJS - Step-by-Step Execution

Concept Flow - Revalidation after mutation

User triggers mutation

↓

Mutation function runs

↓

Data changes on server

↓

Trigger revalidation

↓

Next.js fetches fresh data

↓

Page updates with new data

↓

Done

This flow shows how after changing data (mutation), Next.js re-fetches fresh data to update the page.

Execution Sample

NextJS

async function updateData() {
  await mutate('/api/data', async () => {
    await fetch('/api/data', { method: 'POST' });
    return fetch('/api/data').then(res => res.json());
  }, { revalidate: true });
}

This code updates data on the server and then revalidates the cache to update the page.

Execution Table

Step	Action	Server Data State	Cache State	Page State
1	User triggers updateData()	Original data	Cached original data	Page shows original data
2	POST request sent to /api/data	Data updated on server	Cached original data	Page shows original data
3	Fetch fresh data after POST	Data updated on server	Cache updated with fresh data	Page shows fresh data
4	Revalidation triggered	Data updated on server	Cache updated with fresh data	Page shows fresh data
5	Done	Data updated on server	Cache fresh	Page shows updated data

💡 Revalidation completes, cache and page show updated data

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Server Data	Original data	Updated data	Updated data	Updated data	Updated data
Cache	Original data	Original data	Fresh data	Fresh data	Fresh data
Page	Shows original data	Shows original data	Shows fresh data	Shows fresh data	Shows fresh data

Key Moments - 2 Insights

Why does the page still show old data right after the POST request?

Because the cache is not updated immediately after the POST; it updates after fetching fresh data (see Step 2 and 3 in execution_table).

What triggers the page to update with new data?

The revalidation process updates the cache with fresh data, which causes the page to re-render with updated content (see Step 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the cache state right after the POST request (Step 2)?

A Cache has fresh updated data

B Cache still has original data

C Cache is empty

D Cache has corrupted data

💡 Hint

Check the 'Cache State' column at Step 2 in execution_table

At which step does the page start showing the updated data?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look at the 'Page State' column in execution_table

If revalidate option was false, what would happen to the page state after mutation?

A Page would never update automatically

B Page would show an error

C Page would update immediately

D Page would reload the whole app

💡 Hint

Think about the role of revalidation in updating cache and page

Concept Snapshot

Revalidation after mutation in Next.js:
- Mutation changes data on server
- Cache still holds old data initially
- Revalidation fetches fresh data
- Cache updates with fresh data
- Page re-renders showing updated content
Use mutate() with { revalidate: true } to trigger this flow.

Full Transcript

In Next.js, when you change data on the server using a mutation, the page does not update immediately because the cached data is still the old version. After the mutation, Next.js triggers a revalidation process that fetches fresh data from the server and updates the cache. Once the cache updates, the page re-renders to show the new data. This process ensures the user sees the latest information without a full page reload. Using the mutate function with the revalidate option set to true controls this behavior.