Update docs on supported file extensions

[ksmithut]

This adds support for common js files using the ES Module interop spec.

This is for projects who have "type": "module" in their package.json, normal .js files fail to load saying that you need to use import. json and yaml work just fine, but in the cases like with typescript where you need to run tsc without passing in file parameters, the only way to do that is with the .js files.

Using the .cjs extension forces it to load as a common js file and works correctly even in es-module enabled projects.

I'm also happy to update the documentation, but the documentation didn't refer to the other possible extensions mentioned in this file, so I'll wait until I hear back.

[iiroj]

Thanks for the PR! LGTM, but for some reason Yarn is having troubles when running the tests (not related to this).

Does our readme link to cosmiconfig's, where the extensions are listed? I think having the filenames listed in our readme could only help!

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[ksmithut]

It does link to cosmiconfig's docs, but because there is a static list of searchPlaces in your code, it doesn't include everything that cosmiconfig supports unless you opt into it. Another option would be to remove the searchPlaces option and just use the default: https://github.com/davidtheclark/cosmiconfig#searchplaces which looks like this at the time of writing:

[
  'package.json',
  `.${moduleName}rc`,
  `.${moduleName}rc.json`,
  `.${moduleName}rc.yaml`,
  `.${moduleName}rc.yml`,
  `.${moduleName}rc.js`,
  `.${moduleName}rc.cjs`,
  `${moduleName}.config.js`,
  `${moduleName}.config.cjs`,
]

But then you don't have as much control. I imagine that if you gave a module name of lint-staged it would use .lint-stagedrc instead of what you have now without the dashes. I don't think new file formats will come up too often, so I think it's fine as it is.

Maybe the wording should be changed where it says:

See cosmiconfig for more details on what formats are supported.

to something more like:

We use cosmiconfig. If we're missing a file format they support, let us know.

Since it is configured to be with a list of searchPlaces, you won't automatically get all of the file extensions that cosmiconfig supports.

[iiroj]

It looks like there is a prior MR doing the same thing: #909

[iiroj]

I merged the other PR, but if you want still want to update the README, that would be nice. 👍

[iiroj]

Thanks a lot for the PR, I appreciate it!

[github-actions]

🎉 This PR is included in version 10.4.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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[ksmithut]

You bet, thank you for the awesome tool :)