Fast Refresh is a new React feature that immediately rerenders components when you make changes to your code in an editor. With Fast Refresh, your browser view updates without losing component state, which leads to a better developer experience.
Fast Refresh is a new iteration on hot reloading. Hot reloading was intended to have similar benefits, but it didn't work well with functional components and hooks. It also didn't handle errors well, so you'd have to restart your app after making a typo. Fast Refresh improves on those shortcomings.
- Dan Abramov explains Fast Refresh in a GitHub PR comment
- Difference between hot reloading and fast refresh (Stack Overflow)
- Fast Refresh announcement on the React Native blog
- React Fast Refresh — The New React Hot Reloader Medium article by Michael Chang