[Bug]: loading jest.config.ts results in "Unexpected token 'export'"

[lppedd]

Version

30.0.5

Steps to reproduce

This is a follow up to #15682, since that one is closed.
As far as I understand, an attempt to fix the problem was made in #15694.

Under Node.js 22.18, loading a jest.config.ts with ESM syntax under CommonJS results in the following error:

---

And this Node.js warning:

Warning: Failed to load the ES module: C:\Users\edoardo.luppi\IdeaProjects\client-vscode\client-shared\ts\jest.config.ts. Make sure to set "type": "module" in the nearest package.json file or use the .mjs extension

---

This is the code flow for the code path that was changed in #15694 and #15720.

jest-debug.mp4

Expected behavior

It should load the TS file without erroring out.

Actual behavior

It throws an error.

Can be workarounded by using --no-experimental-strip-types.

Additional context

No response

Environment

System:
  OS: Windows 10 10.0.19045
  CPU: (8) x64 Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
Binaries:
  Node: 22.18.0 - C:\Program Files\nodejs\node.EXE
  Yarn: 1.22.22 - ~\AppData\Roaming\npm\yarn.CMD
  npm: 10.9.3 - C:\Program Files\nodejs\npm.CMD
  pnpm: 9.5.0 - ~\AppData\Roaming\npm\pnpm.CMD
npmPackages:
  jest: 29.7.0 => 29.7.0

Note that the Jest code I'm debugging is from 30.0.5, even tho I currently have 29.7.0 mentioned in my package.json file.

[lppedd]

I guess the fix was simply wrapping the error? I see tests get executed anyways, which is good.
However, what about the warning? Should we simply ignore it?

[hainenber]

@lppedd you should install ts-node as dev dep in your project, as described by the Config section.

[lppedd]

@hainenber it is installed as a dev dependency, I don't think it depends on that.

[hainenber]

ts-node is pretty much the loader serving as fallback for jest.config.ts without native lightweight Typescript support in Node 23.0 so yeah, it's actually a crucial dep.

Having said that, from the video, the config is actually loaded so it's not due to ts-node not yet added, my fault for that one. Can you post the error/stack trace from running Jest in the project?