React

React 19.3 adds new APIs (addTransitionType) for driving View Transition animations, support for refs on Fragments, and a react-dom browser() API that lets a subtree render only in the browser without producing a recoverable server-rendering error, plus an onBrowserBailout option to observe when this happens. It also changes transition scheduling so transitions render independently instead of being entangled into a single render, meaning a slow transition no longer blocks unrelated ones.

Matters for: Useful for teams building animated page or view transitions in React DOM apps and for engineers doing server-side rendering with components that must defer certain logic to browser-only environments.