unstable_after

unstable_after allows you to schedule work to be executed after a response (or prerender) is finished. This is useful for tasks and other side effects that should not block the response, such as logging and analytics.

It can be used in Server Components (including generateMetadata), Server Actions, Route Handlers, and Middleware.

The function accepts a callback that will be executed after the response (or prerender) is finished:

import { unstable_after as after } from 'next/server'
// Custom logging function
import { log } from '@/app/utils'
 
export default function Layout({ children }: { children: React.ReactNode }) {
  after(() => {
    // Execute after the layout is rendered and sent to the user
    log()
  })
  return <>{children}</>
}

Good to know: unstable_after is not a Dynamic API and calling it does not cause a route to become dynamic. If it's used within a static page, the callback will execute at build time, or whenever a page is revalidated.

Reference

Parameters

• A callback function which will be executed after the response (or prerender) is finished.

Serverless function duration

unstable_after will run for the platform's default or configured max duration of a serverless function. If your platform supports it, you can configure the timeout limit using the maxDuration route segment config.

Good to know

• unstable_after will be executed even if the response didn't complete successfully. Including when an error is thrown or when notFound or redirect is called.
• You can use React cache to deduplicate functions called inside unstable_after.
• cookies cannot be set inside unstable_after since the response has already been sent.
• Dynamic APIs cannot be called within unstable_after. Call them outside of unstable_after and use the object they returned.
• unstable_after can be nested inside other unstable_after calls, for example, you can create utility functions that wrap unstable_after calls to add additional functionality.

Alternatives

The use case for unstable_after is to process secondary tasks without blocking the primary response. It's similar to using the platform's waitUntil() or removing await from a promise, but with the following differences:

• waitUntil(): accepts a promise and enqueues a task to be executed during the lifecycle of the request, whereas unstable_after accepts a callback that will be executed after the response is finished.
• Removing await: starts executing during the response, which uses resources. It's also not reliable in serverless environments as the function stops computation immediately after the response is sent, potentially interrupting the task.

We recommend using unstable_after as it has been designed to consider other Next.js APIs and contexts.