Middleware trong Next.js App Router là gì?

Middleware là middleware.ts ở root, chạy trên Edge runtime trước mọi request.

• Dùng để: authentication/authorization, redirect, rewrite URL, add/modify headers, A/B testing.
• Return NextResponse để điều khiển response.
• Dùng matcher config để chỉ định routes áp dụng.
• Nhẹ và nhanh vì Edge runtime.

Middleware is a middleware.ts file at the project root that runs on the Edge runtime before every request.

• Use it for: authentication/authorization checks, redirects, URL rewrites, adding/modifying response headers, and A/B testing.
• Return a NextResponse to control the response.
• Use the matcher config to target specific routes.
• It is fast and lightweight because it runs on the Edge.