Looks like they're using Babel and Rollup. https://github.com/facebook/react/blob/main/scripts/rollup/build.js https://github.com/facebook/react/blob/main/scri

Looks like they're using Babel and Rollup. https://github.com/facebook/react/blob/main/scripts/rollup/build.js https://github.com/facebook/react/blob/main/scripts/rollup/b...