Unexpected Behavior using "after" in middleware

[willwill96]

Link to the code that reproduces this issue

https://github.com/willwill96/nextjs-after-function-repro

To Reproduce

1. Start the application
2. Fetch http://localhost:3000 through preferred method
3. Observe Logs for the following

• Middleware Timing - Start {time}
• Middleware Timing - End {time}
• Page Timing - Start {time}
• Page Timing - End {time}

Current vs. Expected behavior

Current Behavior:
after blocks within middleware functions are executed before page render begins

Expected Behavior:
From the docs

after allows you to schedule work to be executed after a response (or prerender) is finished.

Based on this, I expect after blocks within middleware functions to be executed after page render is finished.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP Tue Nov 5 00:21:55 UTC 2024
  Available memory (MB): 47749
  Available CPU cores: 16
Binaries:
  Node: 22.12.0
  npm: 10.9.0
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 15.1.4 // Latest available version is detected (15.1.4).
  eslint-config-next: 15.1.4
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Middleware

Which stage(s) are affected? (Select all that apply)

next dev (local), next start (local), next build (local)

Additional context

Example Application Output:

Middleware Timing - Start 14041.842787
Middleware Timing - End 14042.483035
Page Timing - Start 14060.135459
 GET / 200 in 27ms
Page Timing - End 14069.832975

Relevant code:

• src/middleware.ts

import { after, NextRequest, NextResponse } from "next/server";

export async function middleware(req: NextRequest) {
    if (req.url === 'http://localhost:3000/') {

        console.log("Middleware Timing - Start", performance.now())
        after(()=>{
          console.log("Middleware Timing - End", performance.now())
        })
    }
    return NextResponse.next()
}

• src/app/page.tsx

import { after } from "next/server";

export default function Home() {
  console.log("Page Timing - Start", performance.now())
  after(()=>{
    console.log("Page Timing - End", performance.now())
  })
  return (
    <div className.....
  );
}