Apa sing digunakake middleware Next.js?

Question

Accepted Answer

**Middleware** yaiku kode sing **dijalankan sadurunge permintaan rampung** — ing Edge, sadurunge halaman utawa route handler ngrenda. Iku ngidini sampeyan mriksa lan nulis ulang/ngarahake maneh permintaan, netepake header, utawa mriksa auth kanggo akeh rute ing siji panggonan.

## Defining middleware

```ts
// middleware.ts (at the project root)
import { NextRequest, NextResponse } from "next/server";

export function middleware(req: NextRequest) {
  const token = req.cookies.get("session")?.value;

// protect /dashboard — redirect unauthenticated users to login
  if (req.nextUrl.pathname.startsWith("/dashboard") && !token) {
    return NextResponse.redirect(new URL("/login", req.url));
  }
  return NextResponse.next(); // allow the request to proceed
}

// only run on these paths (performance — don't run on every asset)
export const config = { matcher: ["/dashboard/:path*", "/account/:path*"] };
```

## What middleware can do

```ts
NextResponse.redirect(url);          // send the user elsewhere (auth gates)
NextResponse.rewrite(url);           // serve different content, URL unchanged (A/B, i18n)
NextResponse.next();                  // continue, optionally with modified headers
// req.geo / req.cookies / req.headers — inspect location, auth, etc.
```

Panggunaan umum: **gating autentikasi**, **pengalihan** (adhedhasar lokal/geo, www→apex), **A/B testing** liwat rewrite, netepake **security header**, lan bot/bendera fitur.

## Key constraints

```text
⚠️ Runs on the EDGE runtime → no Node.js APIs (no fs, limited libraries)
⚠️ Must be FAST — it runs before every matched request; heavy work adds latency
⚠️ Can't access the database directly for complex auth — do lightweight checks
   (e.g. verify a JWT/cookie exists); do full auth in the page/handler
```

Konfigurasi `matcher` penting: watesan middleware menyang mung rute sing butuh, supaya ora urun ing aset statis lan nyedhot kabeh.

## Napa iku penting

Middleware minangka titik pengontrol tunggal kanggo logika permintaan lintas — ngarahake maneh autentikasi, rute lokal, rewrite, lan header — diterapake ing akeh rute tanpa mbaleni kode ing saben kaca.

Kaandhanane Edge (cepet, ora ana API Node, mung pariksa rada) lan scoping `matcher` apa sing ngidini sampeyan nggunakake kanthi bener kanggo gatekeeping lan rute.