What's New in React: A Revolution for Frontend Developers

React 19, the latest version of the popular JavaScript library, introduces major features and optimizations, significantly improving the experience for developers and end users. Here is an overview of the most notable innovations.

Feature overview

⚛️React Compiler
?️ Server components ?
?Automatic batch processing?
?️SEO metadata
?Improved data recovery with Suspense
? Loading assets
? Improved hooks

⚛️ React Compiler ⚛️

React19 has a new wizard called React Compiler?. It's like a smart code compiler that makes your code run faster without you having to do any extra work. This means that people who build websites can write simpler code, and the compiler will make sure it works really well. It's like having a super smart assistant that cleans and organizes your room for you, so you can focus on the game and have fun with React!

?️ Server components?

React19 comes with the “Server Components” superpower.

It's like having a smart rendering tool that does part of the work before you even ask!

React19 renders UI components on the server, regardless of your client-side application or traditional server-side rendering (SSR) setup. By pre-rendering components on the server, CSRs can automatically improve page load times.

This means that when you open a website, images and words appear much faster. This is especially useful for websites with lots of cool features. The best part is that these server components can work in different ways depending on the needs of the website.

Code example: Server components

File: ServerComponent.server.js

This React component is a Server Component. This means that it is rendered on the server side before being sent to the client. Server-side rendering is particularly useful for:

1. Improve performance: Data is generated server-side, which reduces the load on the client.

2. SEO: The generated content is directly visible to search engines.

This component is suffixed with .server.js, which indicates that it is intended for server rendering only. React uses this convention to distinguish components rendered server-side from those rendered client-side.

File: App.client.js

• Importing ServerComponent
  The ServerComponent (server-side rendered) is imported into the client-side React application.

• App Component
  The App component is a Client Component, intended to be rendered client-side. It includes the ServerComponent in its rendering.

• Client-side rendering with ReactDOM
  The createRoot method initializes the application in a DOM element with the root ID. Next, the App component (and by extension, its child components) is rendered.

How does it work?

1. Server side:
   ServerComponent.server.js is rendered on the server, generating static HTML that is sent to the client.

2. Client side:
   Once the content is received, React hydrates the application, adding customer interactivity.

Why use Server Components?

1. Performance optimization
   Heavy calculations or API calls are handled server-side, reducing latency for the end user.

2. Ease of development
   The separation between Server and Client Components allows for better structuring of the application.

3. Flexibility
   React Server Components can be combined with frameworks like Next.js to get the best of both worlds (Static Site Generation Server-Side Rendering).

?Automatic batch processing?

React 19 introduces automatic batching for all updates in event handlers. This means that multiple state updates in a single event handler will now be batched automatically, resulting in fewer renders and improved performance.

Code example: automatic batch processing

?️SEO metadata?

React 19 now has an AutoSEO feature that helps find websites on the Internet! Now React makes SEO-sensitive elements simple and you can easily control titles, descriptions, and other SEO-relevant elements right in your React app. This way, when someone searches for something on the Internet, they can find the right websites faster.

?Improved data recovery with Suspense

React 19 leverages the Suspense feature to make data retrieval simpler and more intuitive. With new data recovery capabilities, you can now handle asynchronous operations more elegantly within your components.

Code Example: Data Recovery with Suspense

? Loading assets

React 19 has a feature where assets automatically load in the background so websites run faster and look better!

It starts loading images and other elements for the next page while you are still viewing the current page. This means that when you click to go to a new page, it displays very quickly!

Have you ever seen a website that looked weird for a split second when it first loaded? Like the words aren't in the right place or the colors are mixed up? React 19 also fixes this issue. He makes sure everything looks right before showing it to you.

Code example: simultaneous rendering

This way the website can load elements in the background without disturbing you while you are using it. Focus on what matters.

Hooks

React 19 introduces new hooks to help handle optimistic UI events and updates more efficiently. The useEvent hook provides a simpler way to handle event listeners, while the useOptimistic hook helps handle optimistic UI states.

Code example: hook useEvent

Code example: hook useOptimistic

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