cloudflare-module + rolldown runtime fails when ESM imports CJS that uses require()

[medz]

Environment

Nitro: 3.0.260311-beta
Rolldown: 1.0.0-rc.10
Node.js: v25.2.1
Bun: 1.3.11

Nitro config:

import { defineNitroConfig } from "nitropack/config";

export default defineNitroConfig({
  preset: "cloudflare-module",
  builder: "rolldown",
  serverDir: "server",
});

Reproduction

I can provide a minimal reproduction repo if needed. The local reproduction is very small:

server/lib/cjs-builtin-require.cjs

const { EventEmitter } = require("events");

module.exports = {
  EventEmitter,
  Client: class Client extends EventEmitter {},
};

server/lib/cjs-builtin-require.mjs

import client from "./cjs-builtin-require.cjs";

export default client;

server/routes/api/test.ts

import { defineEventHandler } from "h3";
import builtin from "../../lib/cjs-builtin-require.mjs";

export default defineEventHandler(() => {
  return {
    ok: true,
    clientName: builtin.Client.name,
    eventEmitterType: typeof builtin.EventEmitter,
  };
});

Build and run:

bunx nitro build
bunx wrangler dev --config .output/server/wrangler.json
curl http://127.0.0.1:8787/api/test

Describe the bug

With Nitro main, preset: "cloudflare-module", and builder: "rolldown", a module graph like this fails at runtime:

• ESM route imports an ESM wrapper
• the ESM wrapper imports a CJS file
• the CJS file does require("events")

The build succeeds, but the generated worker output still contains a runtime require("events") path, so the worker fails at runtime.

The minimal issue is that Nitro currently produces an invalid worker/runtime output for ESM -> CJS -> require(node builtin) in cloudflare-module + rolldown.

Additional context

The generated route chunk contains:

const { EventEmitter } = __require("events");

So the build succeeds, but the worker crashes at runtime because require is not available in that environment.

Logs

HTTP/1.1 500
Content-Length: 57
Content-Type: application/json; charset=utf-8

{
  "error": true,
  "status": 500,
  "unhandled": true
}

Wrangler log:

Error: Calling `require` for "events" in an environment that doesn't expose the `require` function. See https://rolldown.rs/in-depth/bundling-cjs#require-external-modules for more details.
    at .../.output/server/_runtime.mjs
    at .../.output/server/_routes/api/test.mjs

[pi0]

#4133 should address this issue as a workaround

Can you please make a new reproduction with nitro-nightly to see what more cases are still unhandled? 🙏🏼

[medz]

I verified this again in two fresh standalone reproductions outside the Nitro repo source tree.

1. nitro-nightly

Using a clean directory with:

• nitro: 3.0.1-20260320-151809-6b52e381 (via npm alias to nitro-nightly)
• preset: "cloudflare-module"
• builder: "rolldown"
• serverDir: "server"

The same minimal case still reproduces:

• ESM route imports ESM wrapper
• ESM wrapper imports CJS file
• CJS file does require("events")

Generated output still contains:

const { EventEmitter } = __require("events");

Requesting /api/test with wrangler dev still returns 500 with:

Error: Calling `require` for "events" in an environment that doesn't expose the `require` function.

2. #4133 pr.new package

I also tested the package from the PR comment:

npm i https://pkg.pr.new/nitro@4133

Using the same standalone reproduction, this case still fails in the same way.

Generated route chunk still contains:

const { EventEmitter } = __require("events");

And wrangler dev still fails at runtime with the same require("events") error.

So at least for this minimal case:

• current nitro-nightly does not fix it
• #4133 does not cover it

It looks like #4133 addresses the createRequire(import.meta.url) path, but not this ESM -> CJS -> require(node builtin) case.

[pi0]

Can you please share a runnable minimal reproduction i can clone/run? 🙏🏼 require(node builtin) should be actually possible in workerd as nitro enables node compat! If it is not we need some workarounds to make sure it will be.

[medz]

Runnable minimal reproduction repo:

https://github.com/medz/nitro-cloudflare-rolldown-require-repro

It is intentionally minimal and reproduces the same case from this issue:

• preset: "cloudflare-module"
• builder: "rolldown"
• ESM route imports ESM wrapper
• ESM wrapper imports CJS
• CJS does require("events")

Run steps:

bun install
bun run build
bun run dev

Then:

curl http://127.0.0.1:8787/api/test

Current result:

• response is 500
• built route chunk contains __require("events")
• wrangler logs Calling require for "events" in an environment that doesn't expose the require function.

[pi0]

Thanks for reproduction! I see issue is with platform and compat date. Changing this config makes reproduction working:

import { defineNitroConfig } from "nitro/config";

export default defineNitroConfig({
  preset: "cloudflare-module",
  builder: "rolldown",
  serverDir: "server",
  rolldownConfig: {
    platform: 'node'
  }
});

I will push a patch to make sure we set proper platform when node compat is on (default) for cf

[medz]

OMG 🤦, it's that simple? I don't think I ever paid attention to the rolldownConfig.platform = "node" configuration before 😂.

Sorry, it seems I overcomplicated things... and overlooked the fundamental details.

[medz]

😢Let's close this issue. I'm so embarrassed today 😭, and this problem has been bothering me for a long time. But I've never paid attention to this parameter, even though I spend every day going through the Nitro and Rolldown source code.

[pi0]

No worries at all and thanks for caring enough for pushing nitro to be better!! Lets wait for #4138 it should remove need for any additional config.

[medz]

While it doesn't fundamentally solve the problem of converting CJS (require) to ESM (import) in rolldown code transformation, CF itself supports using require within ESM.

So, the reason why running wrangler directly works is now clear, haha!