React 16: A look inside an API-compatible rewrite of our front end UI library (code.facebook.com)

> With today's release of React 16, we've completely rewritten the internals of React while keeping the public API essentially unchanged.

After the Angular 1-to-2 letdown, this is a refreshing commitment to keeping a stable API.

This is a really cool engineering article on how they managed the migration of React 16 rewrite.

It illustrates the use of

- feature toggles to reduce merge conflicts

- TDD for api coverage

- regression logging for faster feedback loop

- coverage chart for motivation

- staggered rollout and A/B testing with an eye on product metrics for migration issues

Thanks for sharing!