What’s New in React 19?

With React 19's release, there's a lot to be excited about. This update brings new features and improvements that promise to enhance productivity and performance for developers at all levels.

Improved Server-Side Rendering (SSR)

React 19 has optimized server-side rendering, making it faster and more efficient, which is great for SEO and performance.

import { renderToString } from 'react-dom/server';
import App from './App';

const html = renderToString(<App />);
console.log(html);

Suspense for Data Fetching

Remember having to handle loading states and asynchronous data fetching? Suspense makes this so much easier. It allows components to "wait" for something (like data) before rendering.

import React, { Suspense } from 'react';

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

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

Concurrent Rendering and the New Transition API

Concurrent rendering is a game-changer for performance. Using the startTransition function lets us update state without blocking the UI, ensuring that high-priority updates (like user inputs) are handled immediately without delaying other updates. The Transition API is also a good choice for UI transitions, ensuring smooth and consistent animations.

import React, { useState, useTransition } from 'react';

function App() {
  const [isPending, startTransition] = useTransition();
  const [text, setText] = useState('');

  const handleChange = (e) => {
    startTransition(() => {
      setText(e.target.value);
    });
  };

  return (
    <div>
      <input type="text" value={text} onChange={handleChange} />
      {isPending ? 'Loading...' : <p>{text}</p>}
    </div>
  );
}

New JSX Transform

The new JSX transform simplifies your code, no more need to import React at the top of every file!

// No need to import React from 'react';

function App() {
  return <h1>Hello, world!</h1>;
}

export default App;

Automatic Batching of Updates

React 19 automatically batches multiple state updates, improving performance by reducing unnecessary re-renders.

Enhanced Developer Tools

React DevTools has been updated to provide better debugging and performance profiling, including support for the new React 19 features.

React Server Components

Server Components allow you to render parts of your UI on the server, reducing client-side JavaScript and improving load times. This example from the React docs shows how you can render jsx directly from the server, rather than fetching from a server API and then rendering jsx.

import db from './database';

async function Note({id}) {
  // NOTE: loads *during* render.
  const note = await db.notes.get(id);
  return (
    <div>
      <Author id={note.authorId} />
      <p>{note}</p>
    </div>
  );
}

async function Author({id}) {
  // NOTE: loads *after* Note,
  // but is fast if data is co-located.
  const author = await db.authors.get(id);
  return <span>By: {author.name}</span>;

How to Upgrade to React 19

Upgrading to React 19 is straightforward. Here's a quick guide:

Update Dependencies:

npm install react@19 react-dom@19

Check for Deprecated Features: Review the release notes for any deprecated features and update your code accordingly.
Run Tests: Ensure your test suite passes to catch any breaking changes early.
Monitor Performance: After upgrading, keep an eye on your app's performance and address any issues.

Final Thoughts

React 19 is packed with features that improve both developer experience and app performance. Whether it's concurrent rendering, Suspense, or the new JSX transform, there's a lot to love in this update.

Need help with an existing or new React Application, we can help reach out to us.