[Feature]: Support loading jest.config.ts as ESM

[luxaritas]

🚀 Feature Proposal

• If "type": "module" is set in the package.json, jest.config.ts should be treated as ESM, not CJS
• jest.config.mts and jest.config.cts should be looked for and loaded as ESM and CJS, respectively

Motivation

• This is currently the behavior with jest.config.js, and so ESM vs CJS handling differs between JS and TS configs
• I would like to be able to import ESM libraries in my TS config

Example

No response

Pitch

• Config loading is handled by core
• Module behavior between JS and TS should match

[luxaritas]

Related: #11453

[SimenB]

PR welcome! Logic for config file resolution and reading is in https://github.com/facebook/jest/blob/1919ef13df544a968bd2d32e5d7b8a2a1c4b35d1/packages/jest-config/src/readConfigFileAndSetRootDir.ts

[SimenB]

That said, I don't think anything has changed since #11453 (comment) (i.e. you need a loader). But we should at least find cts as that is supposed to be converted to cjs

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[karlhorky]

@SimenB as a first step, maybe let's get support for jest.config.cts, to avoid the extra ts-node.moduleTypes config for ts-node

Took a quick shot at a PR - does it need anything else? (other than fixing the tests)

• Allow jest.config.cts #14064

Edit: @DerTimonius opened a new PR based on mine, which also fixes the tests:

• Allow jest.config.cts #14070

[SimenB]

https://github.com/jestjs/jest/releases/tag/v30.0.0-alpha.3 for .cts support