Edge Runtime

Edge functions, edge middleware, edge-compatible libraries, and limitations.

Overview

Edge Runtime runs code at CDN edge locations for minimal latency.

Key Concepts

• Edge Functions — Run at the edge, not Node.js
• Edge Middleware — Middleware at the edge
• Web APIs — Use standard Web APIs (Request, Response)
• Limitations — No Node.js APIs, limited packages
• Performance — Sub-millisecond cold starts

Code Examples

// Edge middleware
export const config = {
  matcher: '/api/:path*',
  runtime: 'edge'
};

export async function middleware(request) {
  const response = await fetch(request);
  response.headers.set('x-edge', 'true');
  return response;
}

// Edge API route
// app/api/edge/route.js
export const runtime = 'edge';

export async function GET(request) {
  const { searchParams } = new URL(request.url);
  const query = searchParams.get('q');

  // Use edge-compatible database
  const results = await edgeDB.query('SELECT * FROM items WHERE name = $1', [query]);
  
  return Response.json(results);
}

// Edge-compatible auth
import { jwtVerify } from 'jose';

export async function verifyEdgeToken(token) {
  const secret = new TextEncoder().encode(process.env.JWT_SECRET);
  const { payload } = await jwtVerify(token, secret);
  return payload;
}

Practice

Convert a middleware to Edge Runtime and handle edge-compatible JWT verification.