Exploring React Features, Deprecations, and Breaking Changes

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.

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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 use can only be called within a render function.

4. ref as a Prop

You can now pass refs as props directly, eliminating the need for forwardRef. This change simplifies component composition and makes working with refs more intuitive.

5. Improved Suspense

Suspense now supports sibling pre-warming, which commits fallback components immediately when a sibling suspends. This enhancement boosts performance and user experience in data-heavy applications.

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React DOM Client Enhancements

1. Form Actions

Forms in React are smarter with

action props

, enabling better integration with useFormStatus. Submitting a form automatically resets its state for uncontrolled components.

2. Document Metadata and Resource Optimization

React 19 natively supports rendering document metadata, such as

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