moduleFileExtensions must include 'js'

[Ky6uk]

🐛 Bug Report

After an upgrade to v24.0.0 I got an error moduleFileExtensions must include 'js' even though a project in projects array should get only ts files (ex: jest-runner-tslint).

Expected behavior

moduleFileExtensions can contain only exact extensions if the extension js not using at all.

Run npx envinfo --preset jest --markdown

System:

• OS: macOS 10.14.2
• CPU: (4) x64 Intel(R) Core(TM) i5-4250U CPU @ 1.30GHz

Binaries:

• Node: 11.7.0 - /usr/local/bin/node
• Yarn: 1.13.0 - /usr/local/bin/yarn
• npm: 6.5.0 - /usr/local/bin/npm

npmPackages:

• jest: 24.0.0 => 24.0.0

[jeysal]

Confirmed. For use cases like running TSLint, Jest does not internally need .js, so disallowing it was an undocumented breaking change.

[jeysal]

Breaking change: #7160

[SimenB]

I guess we can check if the runner is jest-runner and only require .js if it is

[jeysal]

Is there a reason why jest-runner can't do this check itself?

[SimenB]

We wanna have valid config come out of normalize and never mutate it. I suppose we can throw in there, but it's weird to throw a config error outside of the config module

[jeysal]

I mean, it's generally valid config, it's just that jest-runner doesn't like it - an external runner would have to complain on its own as well. Alternative would be to let runners declare their mandatory extension, but that seems ridiculously overkill 😅
I'll try moving the check into jest-runner when I have some time :)

[github-actions]

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