- Project-wide configuration
babel.config.json files, with the different extensions (.js, .cjs, .mjs)
- File-relative configuration
.babelrc.json files, with the different extensions (.babelrc, .js, .cjs, .mjs)
package.json files with a "babel" key
For compatibility reasons, .babelrc is an alias for .babelrc.json.
https://stackoverflow.com/questions/60288375/when-to-use-babel-config-js-and-babelrc
https://awdr74100.github.io/2020-03-16-webpack-babelloader/
https://babeljs.io/docs/en/config-files