ReferenceError: process is not defined

Why does process.env work in Node but not in my Worker?

The Cloudflare docs say that in Workers there is no process-level environment, so by default process.env is an empty object, and that it is filled with your variables and secrets only when Node.js compatibility is on and the nodejs_compat_populate_process_env flag is active. That flag is on by default for compatibility dates of 2025-04-01 and later. Code written for Node, or generated by an AI tool that assumed Node, reads process.env everywhere, and a Worker built from a bare Wrangler config does not provide it.

We ran one Worker that reads process.env.SUPABASE_URL and env.SUPABASE_URL, with the value in a .dev.vars file. Only the process.env read changed between configs:

compatibility_date 2025-01-01, no flag        ReferenceError: process is not defined
compatibility_date 2025-04-01, no flag        ReferenceError: process is not defined
compatibility_date 2025-01-01, nodejs_compat  process exists, process.env.SUPABASE_URL is undefined
compatibility_date 2025-04-01, nodejs_compat  process.env.SUPABASE_URL has the value
compatibility_date 2026-08-04, no flag        process.env.SUPABASE_URL has the value

env.SUPABASE_URL had the value in every run.

Where do secrets and environment variables go for a Worker or a Pages project?

For a Worker, the docs say environment variables are on the env parameter of the fetch handler. For secrets, run wrangler secret put: it creates a new version of the Worker and deploys it immediately, and the value cannot be read back in Wrangler or the dashboard. Do not put sensitive values in vars in the Wrangler config. Use a .dev.vars file or a .env file for local development, one of them and not both.

For a Pages Function, the Pages docs read both through context.env. You set them in the dashboard under Settings, Variables and Secrets, or with vars in the Wrangler config, and Production and Preview can hold different values. Wrangler's vars are not inherited by named environments, so each environment needs its own.

npx wrangler secret put SUPABASE_ANON_KEY

// Worker
export default {
  async fetch(request, env) {
    const supabase = createClient(env.SUPABASE_URL, env.SUPABASE_ANON_KEY)
  },
}

// Pages Function
export const onRequest = async (context) => {
  const supabase = createClient(context.env.SUPABASE_URL, context.env.SUPABASE_ANON_KEY)
}

How do I keep process.env because a library reads it?

Turn on Node.js compatibility and use a compatibility date of 2025-04-01 or later, so process.env is filled from your bindings. The docs add two caveats: values you assign to process.env are converted to strings, and with Wrangler or the Cloudflare Vite plugin process.env.NODE_ENV is replaced at build time, so it is not a runtime value. They also advise against replacing the whole process.env object with the env object.

{
  "name": "notes-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-04-01",
  "compatibility_flags": ["nodejs_compat"]
}

Checklist

How to fix it, then check the fix

1. 01
   Find every read of process.env in code that runs in the Worker:

   grep -rn "process\.env" --exclude-dir=node_modules --exclude-dir=dist src functions

2. 02Read the value from the handler instead: env.NAME in a Worker, context.env.NAME in a Pages Function. To read it outside the handler, import { env } from "cloudflare:workers".
3. 03
   Store each secret on the Worker. For local runs, put the same names in .dev.vars or .env and keep that file out of git:

   npx wrangler secret put SUPABASE_ANON_KEY

4. 04If a library needs process.env, add "nodejs_compat" to compatibility_flags and set compatibility_date to 2025-04-01 or later, as in the example above.
5. 05Deploy again and request the route that threw. The ReferenceError is gone, and a missing key now shows as undefined on env, which means the secret was never set on that Worker or Pages environment.

Related

Related guides

• SupabaseVercel"Your project's URL and Key are required to create a Supabase client!" on Vercel: the fixGuide
• VercelWhich env vars does my app read that are missing in Vercel production?Guide
• SupabaseCloudflareToo many subrequests by single Worker invocation.Guide

Sources

Official docs behind this checklist

• Cloudflare Workers, Environment variables
• Cloudflare Workers, Secrets
• Cloudflare Workers, Node.js process
• Cloudflare Workers, Compatibility flags
• Cloudflare Workers, Node.js compatibility
• Cloudflare Pages Functions, Bindings
• Cloudflare Workers, Wrangler configuration
• Cloudflare Workers, Supabase integration

FAQ

FAQ for builders before launch