React 19 is here, bringing a wealth of new features, improvements, and breaking changes. This release redefines how developers handle state management, forms, and server-side rendering while deprecating legacy APIs. If you’re planning to upgrade, buckle up for a transformative journey. This guide will walk you through the highlights of React 19, with tips to ensure a smooth transition.
Highlights of React 19
New Features
1. Actions and useActionState
The startTransition API now supports async functions, referred to as "Actions." Actions can manage state updates, handle side effects like fetch(), and include error handling. They streamline transitions with coordinated state updates and UI rendering.
The new useActionState hook complements this by providing access to Action states, including pending and final states. It accepts a reducer for granular control, making it an essential tool for form interactions and complex state flows.
2. Optimistic Updates with useOptimistic
useOptimistic enables developers to set temporary state changes while a transition is ongoing, providing a smoother user experience. The state reverts or updates automatically once the async operation finishes.
3. use API
React 19 introduces the use API, which allows promises or contexts to be read during render. This can simplify server data fetching workflows but comes with the restriction that can only be called within a render function.