Start with the Babel core Contributing docs.

Fork the babel-polyfills repository to your GitHub Account.

Then, run:

$ git clone https://github.com/<your-github-username>/babel-polyfills
$ cd babel-polyfills
$ yarn

Then you can either run:

$ yarn build

to build the repo once or:

$ yarn watch

to have the repo build itself and incrementally build files on change.

$ yarn lint

$ yarn tscheck

$ yarn test

See docs/polyfill-provider.md.