Web Development is being evolved in every now and then. Every change brings some enhancement in performance and user experiences. The concept of Edge Computing is one of the most significant recent shifts. This post will demystify the Edge Runtime along with edge computing, explain its purpose, highlight its limitations, and discuss the recent developments in Next.js regarding Node.js support in Middleware.
What is Edge Computing?
Edge computing is a way of doing server computation that brings processing power, storage, and analysis closer to where the data is actually created or used, instead of sending everything to a far-away central server or big cloud data center.
Think of the internet/network like a big map:
The center = huge cloud data centers (AWS, Google Cloud, Azure) located in specific regions.
The edge = the "outer borders" closest to you — your phone, a local Wi-Fi router, a nearby cell tower, a small server in a store/factory, or points of presence (PoPs) of CDNs.
Edge computing moves some (or a lot) of the work to these outer/nearby locations → the "edge" of the network.
The "edge" refers to the outer parts of the network — places physically nearer to end-users (CDN points, cell towers, local devices, mini-servers in stores/factories, etc.).
Edge servers are the actual machines/hardware located at those edge locations that run the code/workloads. Edge reduces mainly the network travel time for both directions, plus often execution startup time.
Why bother? Because:
Things happen instantly (no waiting for round-trips) → perfect for self-driving cars that need to brake NOW, video games that feel smooth, or a doctor watching live surgery footage without lag.
You don't send tons of raw data back and forth → saves internet bandwidth and money.
It works even if the internet is spotty → the local part keeps running.
Sometimes it's more private → sensitive info doesn't travel far.
So yeah — cloud is the giant central kitchen, edge is lots of small smart kitchens everywhere near people and devices. That's why apps feel snappier, cars get safer, and factories run smoother in 2026 and beyond. Pretty cool, right?"
What is Edge Runtime?
The Edge Runtime is not the physical edge servers or the global network itself (that's the edge computing infrastructure provided by Vercel, Cloudflare, Fastly, etc.). Instead, it's a very specific, lightweight software runtime — basically a slim JavaScript execution engine — designed on purpose to run inside those edge locations.
Built on the same V8 engine (the super-fast JS engine inside Chrome and Node.js).
But stripped down to only Web Standard APIs (fetch, Request/Response, Streams, Web Crypto, etc.).
Runs in tiny isolated sandboxes called V8 Isolates — no full containers or VMs needed.
No access to full Node.js stuff like fs (filesystem), child_process, native modules that need OS access, or many older Node APIs.
Result: Extremely fast startup (cold starts often < 10 ms, sometimes ~1 ms), tiny memory footprint, secure by default, and perfect for running on hundreds of edge points worldwide without heavy overhead.
Edge Runtime = the lightweight "brain" that actually executes your JavaScript code at the edge locations.
What are Edge functions?
An edge function = any piece of server-side code that you tell Next.js/Vercel to run using the Edge Runtime (that lightweight, fast, global thing we talked about).
The most common and main way to create one in Next.js (especially in the modern App Router) is by writing a Route Handler and adding export const runtime = 'edge';. In practice, edge functions are usually Route Handlers running at the edge. But edge functions can also appear in other places (like Middleware in older setups).
Why "mainly" here? Because Route Handlers are the primary way to build custom server endpoints (like APIs) in Next.js App Router, and opting into 'edge' turns them into edge functions for low-latency global use.
// app/api/hello/route.ts
export const runtime = 'edge'; // ← makes this an edge function
export async function GET(request) {
return Response.json({ message: "Hello from edge!" });
}
Server Components or Server Actions can sometimes opt into edge (with config), but it's uncommon and limited. Mostly, when people say "edge function" in Next.js/Vercel docs, they mean Route Handlers with runtime: 'edge'.
Why Route Handlers Are the "Main" Home for Edge Functions
Route Handlers are built exactly like tiny serverless APIs (GET/POST/etc.).
They use Web standards (Request, Response) — perfect match for the Edge Runtime's limits.
Vercel auto-deploys them globally at the edge when you choose 'edge'.
Great for fast, dynamic stuff: auth checks, geo-personalization, quick proxies, small APIs.
Conclusion
Edge computing moves computation closer to users on a global network of nearby servers, slashing latency and making apps feel instant worldwide.
In Next.js, the Edge Runtime is a lightweight JS engine that lets you run code at these edge locations. Add export const runtime = 'edge' to a Route Handler → it becomes an edge function, executing fast and locally for every visitor.
Trade-off: Speed & reach come with limits (Web APIs only, no heavy Node packages or file system). Use edge for latency-sensitive paths, stick with Node.js runtime for complex logic.
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