Edge functions run your code milliseconds from your users — no round trips to a central server. Learn what moves to the edge, what stays in the cloud, and how to build edge-first architectures.

# Edge Computing for Web Developers: A Practical Introduction Edge computing moves computation from a central data center to nodes geographically close to the user — often within milliseconds. For web developers, this means authentication, personalization, A/B testing, and content rewriting can happen before a request ever reaches your origin server. ## Why Edge? A user in Mumbai hitting a server in us-east-1 adds ~200ms of latency before your code runs. An edge node in Mumbai cuts that to <5ms. Edge functions are also where Wasm shines — sub-millisecond cold starts mean every request gets a fresh, fast execution environment. ## What Belongs at the Edge ✅ Great for the edge: - Auth token validation (verify JWT without hitting your auth service) - Geo-based routing and redirects - A/B testing and feature flag evaluation - Response header manipulation (security headers, caching) - Personalized content rewriting - Rate limiting and bot detection ❌ Keep in the cloud: - Database writes and complex reads (edge has no persistent storage) - Long-running computations - Anything requiring large secrets or service accounts ## A Real Edge Function (Cloudflare Workers) ```typescript export default { async fetch(request: Request): Promise<Response> { const url = new URL(request.url); const country = request.cf?.country ?? "US"; // Geo-redirect at the edge — no origin hit if (url.pathname === "/" && country === "IN") { return Response.redirect("https://example.com/in", 302); } // Validate auth token at the edge const token = request.headers.get("Authorization")?.split(" ")[1]; if (!token || !verifyJWT(token, JWT_SECRET)) { return new Response("Unauthorized", { status: 401 }); } return fetch(request); // pass to origin } }; ``` ## Edge Storage Primitives Modern edge platforms now offer lightweight storage: | Primitive | Use Case | |---|---| | KV Store | Config, feature flags, cached data | | Durable Objects | Stateful coordination (e.g., rate counters) | | R2 / Blob Storage | Assets, user uploads | ## Platform Comparison | Platform | Runtime | Cold Start | |---|---|---| | Cloudflare Workers | V8 isolates + Wasm | <1ms | | Fastly Compute | Wasm (WASI) | ~1ms | | Deno Deploy | V8 | ~2ms | | AWS Lambda@Edge | Node.js | ~100ms | Edge-first architecture is increasingly the default for high-performance web applications. Start with one use case — JWT validation or geo-routing — and expand from there.