Run post-response work after the response

In Next.js, schedule work that the response does not depend on with after(), so it runs after the response is sent.

Implementation

• Use after() for logging, analytics, audit records that may be written late, cache warming, and notifications that the caller does not wait for.
• Keep work in the request when the response reports its result, or when it must succeed before the caller proceeds.
• Handle errors inside the after() callback; the caller cannot see them.
• after() callbacks run even when the response fails or redirects; check the outcome inside the callback when that matters.

Rationale

Every await before a response adds its latency to the request. Work that the caller does not need delays it for no benefit. after() lets the platform finish that work once the response is on its way.

Examples

Incorrect (counterexample):

export async function POST(request: Request) {
  const result = await updateDatabase(request);
  await logUserAction({ action: 'update', userAgent: request.headers.get('user-agent') });
  return Response.json(result);
}

The client waits for the log write.

Correct:

import { after } from 'next/server';

export async function POST(request: Request) {
  const result = await updateDatabase(request);
  const userAgent = request.headers.get('user-agent');

  after(async () => {
    try {
      await logUserAction({ action: 'update', userAgent });
    } catch (error) {
      reportError(error);
    }
  });

  return Response.json(result);
}

Validation

For each awaited call in a request path, ask whether the response needs its result or success. If not, it belongs in after().

Awaiting work whose result the response returns is not a violation.