What are the biggest new features in React 19?

React 19's biggest additions are: the React Compiler (automatic memoisation without useMemo/useCallback), Actions (simplified async state updates from forms), Server Components stable release, useOptimistic for optimistic UI, and use() hook for reading promises and context in render.

Is it worth upgrading to React 19 in 2025?

Yes — especially for new projects. The React Compiler eliminates most manual performance optimisation work. For existing applications, upgrade if you are on React 18 already. The migration from React 18 to 19 is relatively smooth. React 16 or 17 apps should upgrade to 18 first.

How do I upgrade from React 18 to React 19?

Run: npm install react@19 react-dom@19. Address any breaking changes — ReactDOM.render() is fully removed (use createRoot), string refs are removed, and some legacy Context APIs are deprecated. Run the React 19 codemods to automatically fix most issues: npx codemod@latest react/19/migration-recipe.

What is the React Compiler and how does it help?

The React Compiler (formerly React Forget) automatically applies memoisation optimisations to your components and hooks. This means you no longer need to manually write useMemo, useCallback, or React.memo for performance optimisation — the compiler does it at build time, reducing both bundle size and developer cognitive load.

React 19: What's New and How to Upgrade 2025

React 19 new features complete upgrade guide 2025

React 19 is the most significant React release since hooks in React 16.8. The React Compiler alone eliminates years of manual performance optimisation work. Combined with stable Server Components, Actions, and new hooks — React 19 fundamentally changes how you write React applications. Here is everything you need to know.

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Key takeaway: The React Compiler is the headline feature. It removes the need for useMemo, useCallback, and React.memo in most cases by automatically applying optimisations at build time. For large React codebases, this alone is worth the upgrade.

6 Major New Features in React 19

React Compiler

Automatic memoisation at build time. useMemo and useCallback become largely unnecessary — the compiler handles it.

Actions

New pattern for handling async operations from forms. Replaces manual useState + event handlers for most form workflows.

Server Components

Stable in React 19. Components that render exclusively on the server — zero client bundle impact, direct database access.

use() Hook

Read promises and context directly in render — no more useEffect for data fetching in many scenarios.

useOptimistic

First-class optimistic UI support. Update UI immediately while async operation completes in the background.

Document Metadata

Native support for <title>, <meta>, and <link> tags in components — no more react-helmet in most cases.

How to Upgrade to React 19 Step by Step

Update React packages: npm install react@19 react-dom@19
Run the codemod: npx codemod@latest react/19/migration-recipe
Fix breaking changes: Remove ReactDOM.render(), string refs, and legacy Context patterns
Enable the compiler: Add the Babel plugin or Vite plugin for the React Compiler
Test thoroughly: Run your test suite. Check hydration, Suspense boundaries, and async workflows
Remove unnecessary memos: Clean up useMemo/useCallback where the compiler now handles it

React 19 Breaking Changes to Know

ReactDOM.render() removed — Must use createRoot() (available since React 18)
String refs removed — Use useRef() instead of ref="myRef"
Legacy Context API deprecated — Migrate to modern createContext() + useContext()
propTypes removed from core — Use TypeScript or a separate prop-types package if needed