[Feature]: Allow require for pure ESM packages with --experimental-require-module #15275
Description
🚀 Feature Proposal
Allow using require for pure ESM packages. This can be either the default behavior, or enabled by reading the --experimental-require-module Node option, or by having a setting in the config (e.g. allowEsmRequire: true).
Motivation
There's an experimental --experimental-require-module flag in Node 22 and 20.17 that allows using CJS require for pure ESM packages. This is great for CJS projects that cannot migrate to ESM yet (e.g. NestJS projects), because they can use modern versions of pure ESM dependencies.
I was able to make it work by adding babel-jest to the project and configuring it to apply @babel/plugin-transform-modules-commonjs plugin to my specific pure ESM dependency. But of course it's more desirable that this works out of the box.
Example
jest.config.mjs
export default {
testEnvironment: 'node',
testRegex: '\\.spec.js$',
moduleFileExtensions: ['js'],
};package.json
{
"name": "jest-require-esm-repro",
"version": "1.0.0",
"main": "index.js",
"devDependencies": {
"jest": "^29.7.0"
},
"dependencies": {
"nanoid": "^5.0.7"
}
}index.js
const { nanoid } = require("nanoid");
exports.id = nanoid()index.spec.js
const { id } = require('.');
describe('index', () => {
test('should return ID', () =>
expect(typeof id).toBe("string"));
})Running the code ✅
jest-require-esm-repro % node --experimental-require-module
Welcome to Node.js v22.6.0.
Type ".help" for more information.
> const { id } = require('.'); id;
'ErAKzYGR5Jkda5HfVnBKb'
Running Jest ❌
jest-require-esm-repro % node --experimental-require-module node_modules/.bin/jest
FAIL ./index.spec.js
● Test suite failed to run
Jest encountered an unexpected token
Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.
Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.
By default "node_modules" folder is ignored by transformers.
Here's what you can do:
• If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to enable it.
• If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript
• To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
• If you need a custom transformation specify a "transform" option in your config.
• If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.
You'll find more details and examples of these config options in the docs:
https://jestjs.io/docs/configuration
For information about custom transformations, see:
https://jestjs.io/docs/code-transformation
Details:
~/jest-require-esm-repro/node_modules/nanoid/index.js:1
({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){import { webcrypto as crypto } from 'node:crypto'
^^^^^^
SyntaxError: Cannot use import statement outside a module
> 1 | const { nanoid } = require("nanoid");
| ^
2 |
3 | exports.id = nanoid()
4 |
at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1505:14)
at Object.require (index.js:1:20)
at Object.require (index.spec.js:1:16)
Test Suites: 1 failed, 1 total
Tests: 0 total
Snapshots: 0 total
Time: 0.14 s, estimated 1 s
Ran all test suites.
Pitch
Jest includes its own module resolution system. Lack of ESM require makes it not on par with Node's module resolution system, meaning that even if I can make the runtime code work with native Node, I have include some sort of transformations to make it work with Jest.