What runtimes does Next.js support (Node.js vs Edge runtime)?

Q: What runtimes does Next.js support (Node.js vs Edge runtime)?

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity. **Difficulty:** Medium > **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified block says which version it ran on. ## 1. Why This Even Matters — A Story First Think of two kitchens. The Node.js kitchen is a full restaurant kitchen with every appliance. The Edge kitchen was a food truck parked near each neighbourhood: quick to reach, but with a small menu because there is no room for the big appliances. Next.js 16.3 started retiring the food trucks and recommending the full kitchen, with caching to make the food arrive quickly anyway. ## 2. The Core Idea 📌 **Interview term

The problem

Question presented to candidate: "What is the difference between the Node.js and Edge runtimes in Next.js, when would you have chosen Edge, and what is the recommendation today?"

What a strong answer should cover:

Node.js runtime: the default for pages, layouts, Route Handlers and, in Next.js 16, Proxy; full Node APIs and npm compatibility.
Edge runtime: a smaller runtime based on Web APIs, historically chosen for low latency and fast cold starts close to users.
Edge limits: no Node built-ins such as fs, restricted packages, size limits; the lab showed process.versions missing.
The Edge runtime is deprecated (16.3.4 and 16.4.2 both warn at build time), and on a page it disables static generation; with Cache Components any runtime export, even 'nodejs', fails the build.
The recommendation is the Node.js runtime everywhere, including proxy.ts, which now runs on Node by default.

Clarifying questions expected:

"Does the code need Node APIs or native packages?" — they only work on Node.js.
"Is the goal latency?" — caching and static rendering usually beat moving compute.

Code / implementation expected: Optional — the runtime export and what the build says.

nextjs
edge-runtime
nodejs-runtime
deployment

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity. Difficulty: Medium

How to read this doc: Each idea is explained in plain language first, then tagged with 📌 Interview term:. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the Verified section, against real output from a build or a running server; each Verified block says which version it ran on.

1. Why This Even Matters — A Story First

Think of two kitchens. The Node.js kitchen is a full restaurant kitchen with every appliance. The Edge kitchen was a food truck parked near each neighbourhood: quick to reach, but with a small menu because there is no room for the big appliances. Next.js 16.3 started retiring the food trucks and recommending the full kit

The solution is hidden so you can try first

5 min read · 8 sections

Read the code

Removing the edge runtime and moving middleware to proxy

// Before (Next.js 14/15)
// app/api/geo/route.ts
export const runtime = "edge";
export async function GET() { return Response.json({ ok: true }); }

// After (Next.js 16): no runtime export, Node.js by default
export async function GET() { return Response.json({ ok: true }); }

// middleware.ts -> proxy.ts   (npx @next/codemod@canary middleware-to-proxy .)
import { NextRequest, NextResponse } from "next/server";
export function proxy(req: NextRequest) {
  return NextResponse.next();
}

Discussion

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