Default to eslint.config.js when syntax-detection is supported

[kecrily]

We could also consider implementing a check in @eslint/create-config during init to verify whether the Node version supports this feature, then determine the output extension accordingly.

Originally posted by @kecrily in #20129

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On some Node.js versions¹, syntax-detection feature can determine if a file is an ES Module (ESM). This means it's not necessary to use an .mjs extension for an ESM-style eslint.config.* file, even in a CJS environment (i.e., a project with no "type" field in package.json).

If the feature is supported but "type" is set to "commonjs", should we still create an ESM-style eslint.config.js?

Footnotes

1. v22.7.0 and v20.19.0 enabled by default ↩

[aladdin-add]

related: #206