Next.js Edge Runtime

Answer

The Edge Runtime is a lightweight runtime that runs Next.js code at the edge (CDN locations closest to users), providing lower latency than traditional serverless functions.

Edge vs Node.js Runtime

Using Edge Runtime

// Route handlers
// app/api/hello/route.js
export const runtime = "edge";

export async function GET(request) {
	return new Response("Hello from the Edge!");
}

// Middleware (always edge)
// middleware.js
export function middleware(request) {
	// Runs at edge automatically
}

// Pages/Server Components
// app/page.js
export const runtime = "edge";

export default function Page() {
	return <div>Edge-rendered page</div>;
}

Edge Limitations

// ✅ Available at Edge
fetch()
Request, Response
URL, URLSearchParams
TextEncoder, TextDecoder
crypto
Streams
setTimeout, setInterval

// ❌ NOT available at Edge
fs (file system)
path
require() dynamic imports
Native Node.js modules
Most npm packages with native bindings
Full Node.js crypto (limited subset available)

When to Use Edge

Use Case	Runtime
Auth checks	Edge ✅
A/B testing	Edge ✅
Geolocation routing	Edge ✅
Simple API responses	Edge ✅
Database queries	Node.js ✅
File operations	Node.js ✅
Heavy computation	Node.js ✅
Third-party SDKs	Node.js ✅

Edge Functions Examples

// Geolocation personalization
export const runtime = "edge";

export async function GET(request) {
	const country = request.geo?.country || "US";
	const city = request.geo?.city || "Unknown";

	return Response.json({
		message: `Hello from ${city}, ${country}!`,
		country,
		city,
	});
}

// A/B Testing
export const runtime = "edge";

export function middleware(request) {
	const bucket = Math.random() < 0.5 ? "control" : "experiment";

	const response = NextResponse.next();
	response.cookies.set("ab-bucket", bucket);

	return response;
}

Edge with ORM/Database

// Use edge-compatible database clients
import { PrismaClient } from "@prisma/client/edge";
import { withAccelerate } from "@prisma/extension-accelerate";

export const runtime = "edge";

const prisma = new PrismaClient().$extends(withAccelerate());

export async function GET() {
	const users = await prisma.user.findMany({
		cacheStrategy: { ttl: 60 },
	});
	return Response.json(users);
}

// Or use edge-native databases
// - Cloudflare D1
// - PlanetScale (HTTP)
// - Neon (HTTP)
// - Turso

Streaming from Edge

export const runtime = "edge";

export async function GET() {
	const encoder = new TextEncoder();

	const stream = new ReadableStream({
		async start(controller) {
			for (let i = 0; i < 5; i++) {
				await new Promise((r) => setTimeout(r, 1000));
				controller.enqueue(encoder.encode(`Data ${i}\n`));
			}
			controller.close();
		},
	});

	return new Response(stream, {
		headers: { "Content-Type": "text/plain" },
	});
}

Edge vs Serverless Comparison

Aspect	Edge	Serverless (Node.js)
Cold start	~0ms	250ms-1s
Location	CDN edge	Regions
Max execution	30s	300s
Memory	Limited	Up to 3GB
APIs	Web Standard	Full Node.js
Use case	Simple, fast	Complex ops

Key Points

• Edge runs at CDN locations for minimal latency
• Near-zero cold starts
• Use Web Standard APIs (fetch, Response, etc.)
• No Node.js-specific APIs (fs, etc.)
• Perfect for auth, A/B tests, redirects
• Use Node.js for database operations with native drivers
• Middleware always runs on Edge