What’s New in React 19? A Quick Guide with Code Examples

React 19 has arrived, bringing new features that make our apps faster and smarter while making development smoother. Here’s a quick look at the top highlights, complete with code snippets to get you started. 🚀

1. Enhanced Server Components

Server Components are now easier to use and more powerful. You can mix server-rendered and client-rendered components seamlessly.

Here’s a simple example:

// Server Component
export default function ServerComponent() {
  return <div>This is rendered on the server!</div>;
}

// Client Component
import ServerComponent from './ServerComponent';

export default function ClientComponent() {
  return (
    <div>
      <ServerComponent />
      <p>This part is interactive on the client.</p>
    </div>
  );
}

Result: Faster initial load times and better interactivity.

2. Smarter Concurrent Rendering

React 19 fine-tunes concurrent rendering. With useTransition, you can prioritize urgent updates while deferring others.

Example:

const [isPending, startTransition] = useTransition();

function handleClick() {
  startTransition(() => {
    setExpensiveState(someLargeData);
  });
}

Users won’t experience lag while React processes updates in the background.

3. Auto-Bundling for Lazy Components

Lazy-loading components is now simpler with auto-bundling, which ensures that only the required code is loaded.

Example:

const LazyComponent = React.lazy(() => import('./LazyComponent'));

function App() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <LazyComponent />
    </Suspense>
  );
}

No extra configurations—React handles the bundling for you!

4. Faster Hydration

Hydration is now selective, meaning React hydrates only what’s visible first. No extra code is needed—it’s enabled out of the box.

// In React 19, hydration automatically prioritizes critical content:
ReactDOM.hydrateRoot(document.getElementById('root'), <App />);

This speeds up interactivity for users with large apps.

5. New Hooks: useOptimistic and useEvent

useOptimistic hook simplifies optimistic UI updates by managing temporary state.
Example:

const [optimisticLikes, setOptimisticLikes] = useOptimistic(0, (prev, newLike) => prev + newLike);

function handleLike() {
  setOptimisticLikes(1); // Update UI instantly
  postLikeToServer();    // Sync with server in the background
}

Instant feedback for users, even with slow network responses.

useEvent helps with stable event handlers, avoiding unnecessary re-renders.
Example:

const handleClick = useEvent(() => {
  console.log('Button clicked!');
});

<button onClick={handleClick}>Click me!</button>

Cleaner code and improved performance in scenarios with frequent event handling.

Conclusion

React 19 is all about speed, efficiency, and developer happiness. From smarter hydration to exciting new hooks.

What feature are you most excited about? Share your thoughts in the comments!

More features https://react.dev/blog/2024/04/25/react-19