unstable_after (Experimental)

This API is experimental and subject to change.

unstable_after() allows you to schedule work to be executed after a response 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.

To use unstable_after(), you need to enable it using the experimental.after config in the next.config.js file:

const nextConfig = {
  experimental: {
    after: true,
  },
}
module.exports = nextConfig

The function accepts a callback that will be executed after the response is finished:

import { unstable_after as after } from 'next/server'
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() will be executed even if the response didn't complete successfully. Including when an error is thrown or when notFound() or redirect() is called.
• unstable_after() is a dynamic function that will opt a route into dynamic rendering. This behavior can be overridden with the export dynamic = "force-static" segment config.
• 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.
• unstable_after() can be nested inside other unstable_after() calls.

Parameters

• A callback function which will be executed after the response is finished.

Returns

• unstable_after() does not return a value.

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.

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.