require() is not available in Workers. Attempted to require:

Error message

require() is not available in Workers. Attempted to require: ${id}

What it means

createRequire in lib/shims/node-module.ts implements require() against a fixed allowlist of Node builtins (fs, path, vm, stream, etc.). Workers cannot synchronously load arbitrary npm packages, so any require('<non-builtin>') throws, embedding the offending id in the message. ESM imports still work normally — only CJS require of third-party packages fails.

Source

Thrown at lib/shims/node-module.ts:194

    'fs/promises': fs_promises,
    'node:stream/promises': stream_promises,
    'stream/promises': stream_promises,
    'node:stream/web': stream_web,
    'stream/web': stream_web,
    'node:util/types': util_types,
    'util/types': util_types,
    'node:timers/promises': timers_promises,
    'timers/promises': timers_promises,
    'node:vm': vmShim,
};

export function createRequire(_filename: string | URL) {
    return function require(id: string): unknown {
        if (Object.hasOwn(builtinModules, id)) {
            return builtinModules[id];
        }
        // For non-builtin modules, throw an error
        throw new Error(`require() is not available in Workers. Attempted to require: ${id}`);
    };
}

export default {
    createRequire,
};

View on GitHub (pinned to bed535e087)

Solutions

Convert the consumer to an ESM import so the bundler resolves the package at build time.
Bundle the needed package (mark it non-external) so Workers receives it statically.
Avoid createRequire-based plugin loading under Workers.
Run the affected route on the Node target where real require() is available.

Example fix

// before
const { createRequire } = require('module');
const req = createRequire(__filename);
const lib = req('some-cjs-pkg');
// after
import someCjsPkg from 'some-cjs-pkg'; // resolved by the bundler at build time

Defensive patterns

Strategy: validation

Validate before calling

// before calling createRequire().require(id), check the allowlist
import { builtinModules } from 'module'; // Node-only reference; under Workers the shim holds the map
const ALLOWED = new Set(Object.keys(builtinModules));
function canRequire(id: string): boolean {
  return ALLOWED.has(id);
}
if (!canRequire(id)) {
  // do not require(); use a static ESM import instead
}

Type guard

function isWorkersRequireError(e: unknown): e is Error {
  return e instanceof Error && /require\(\) is not available in Workers/.test(e.message);
}

Try / catch

try {
  return createRequireFn(id);
} catch (e) {
  if (isWorkersRequireError(e)) {
    // fall back to an ESM-imported module resolved at build time
    return bundledModule;
  }
  throw e;
}

Prevention

Prefer ESM imports over createRequire for third-party packages under Workers.
Bundle (non-externalize) any package a CJS dep needs so the bundler resolves it.
Never use require() for plugin loading of npm packages under Workers.

When it happens

Trigger: A dependency using module.createRequire(filename) to load a CJS third-party (non-builtin) module at runtime under Workers. The id is anything not present in builtinModules (e.g. a package name or relative path).

Common situations: JSDOM or similar libs calling require() on a sub-package; a CJS shim probing for an optional dependency via require(); code ported from Node that uses createRequire for plugin loading.

Related errors

AI-assisted analysis of DIYgod/RSSHub@bed535e087 (2026-08-12). Data as JSON: /api/errors/3b89e380c2cfdc35. Report an issue: GitHub.