Support .cjs file

[ergofriend]

Summary

• Create React App's jest (react-scipts) can not import esm(.mjs) package.
  • like this, Use in create-react-app - Ant Design
• For pass the test with react-merge-refs, it has to export .cjs file.
• Probably, the module bundler does not affect the "module": "./dist/index.mjs", (ESM) loading priority over "main": "./dist/index.cjs".

Test plan

No diff in src.

[gregberge]

Hello @ergofriend, I don't want to expose cjs at all (size of package, dual package hazards..). I found a way to make it work with Jest. Don't know if it works with create-react-app without any config, but it could work. I use Jest on my side and I just had to make it parsed by Babel.

[cascornelissen]

@gregberge, do you have an example of how you use it with Jest? We're running into similar issues here as well and we're interested in a solution ❤️

---

For future reference, we ended up adding the following to our shared Jest configuration, along with adding mjs to moduleFileExtensions.

transform: {
    '^.+\\.mjs$': [require.resolve('babel-jest'), {
        presets: [require.resolve('@babel/preset-env')]
    }],
    // ...
}

[gregberge]

Yeah that's the best thing to do. Until Jest supports ESM completely. That's how I handle it too.