Next Friday Next.js

Rules specific to Next.js applications.

Environment Variables

Client Components

Client components must use NEXT_PUBLIC_ prefix for environment variables.

// Bad:
"use client";

const apiUrl = process.env.API_URL;
const secretKey = process.env.SECRET_KEY;

// Good:
"use client";

const apiUrl = process.env.NEXT_PUBLIC_API_URL;
const appName = process.env.NEXT_PUBLIC_APP_NAME;
const isDev = process.env.NODE_ENV === "development"; // NODE_ENV is OK

No Fallback Values

Disallow fallback values for environment variables. Fail explicitly instead.

// Bad:
const apiUrl = process.env.API_URL || "http://localhost:3000";
const timeout = process.env.TIMEOUT ?? "5000";

// Good:
const apiUrl = process.env.API_URL;
const timeout = process.env.TIMEOUT;

if (!apiUrl) {
  throw new Error("API_URL environment variable is required");
}

Quick Reference