Exploring the Exciting New Features in React 18

React 18 is a significant update for one of the most popular JavaScript libraries used for building user interfaces. This version introduces several exciting new features and improvements that aim to enhance performance, improve the developer experience, and enable new use cases. In this post, we’ll explore some of the standout features of React 18 and what they mean for developers.

Concurrent Rendering

One of the most anticipated features in React 18 is Concurrent Rendering. This new rendering mechanism allows React to prepare multiple versions of the UI at the same time. This can improve the user experience by making the UI more responsive and fluid, especially in applications with complex, interactive interfaces.

Concurrent Rendering enables React to interrupt and pause work, then continue later. This means your app can stay responsive even during heavy rendering tasks. For example, if a user interaction is more urgent, React can prioritize rendering that over less critical tasks.

import { useState, useTransition } from 'react';

function App() {
  const [isPending, startTransition] = useTransition();
  const [input, setInput] = useState('');
  const [list, setList] = useState([]);

  const handleChange = (e) => {
    setInput(e.target.value);
    startTransition(() => {
      const newList = Array(5000).fill(e.target.value);
      setList(newList);
    });
  };

  return (
    <div>
      <input type="text" value={input} onChange={handleChange} />
      {isPending ? 'Loading...' : list.map((item, index) => <div key={index}>{item}</div>)}
    </div>
  );
}

Automatic Batching

React 18 introduces Automatic Batching, which optimizes the way updates are processed. Previously, React batched state updates that occurred within event handlers. However, updates that happened outside of event handlers, like those in setTimeouts or native event listeners, weren’t batched.

With React 18, all updates are automatically batched, regardless of where they originate. This leads to fewer renders and better performance:

// Before React 18
setTimeout(() => {
  setCount(count + 1);
  setFlag(flag + 1);
  // Two separate renders
}, 1000);

// With React 18
setTimeout(() => {
  setCount(count + 1);
  setFlag(flag + 1);
  // Only one render
}, 1000);

New Suspense Features

React’s Suspense feature, which was introduced earlier, has received significant updates in React 18. Suspense allows components to “wait” for something before they render. This is particularly useful for handling asynchronous data fetching.

In React 18, Suspense works seamlessly with Concurrent Rendering to make data fetching more efficient and the UI more resilient. For example, you can now use Suspense to control loading states more granularly, ensuring that your application remains responsive and visually consistent:

import React, { Suspense } from 'react';

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

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

Transitions

Transitions in React 18 allow developers to distinguish between urgent and non-urgent updates. This is particularly useful for distinguishing between interactions that need immediate feedback (like typing in a text box) and those that can be deferred (like loading a new page).

The new useTransition hook lets you mark updates as transitions, allowing React to keep the UI responsive during non-urgent updates:

import { useTransition } from 'react';

const [isPending, startTransition] = useTransition();

startTransition(() => {
  setState(newState);
});

startTransition API
The startTransition API complements the useTransition hook by allowing developers to mark updates as transitions. This helps React prioritize urgent updates over non-urgent ones, ensuring a smooth user experience.

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

function App() {
  const [count, setCount] = useState(0);

  const handleClick = () => {
    startTransition(() => {
      setCount(c => c + 1);
    });
  };

  return (
    <div>
      <button onClick={handleClick}>Increment</button>
      <p>{count}</p>
    </div>
  );
}

Improved Server-Side Rendering

React 18 brings significant improvements to Server-Side Rendering (SSR) with the introduction of a new API called react-dom/server. This API allows for more efficient streaming of HTML, which can improve the performance of server-rendered React applications.

The new streaming SSR architecture lets the server send content to the client as soon as it’s ready, rather than waiting for the entire component tree to be rendered. This can lead to faster load times and a better user experience.

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

const app = express();

app.get('/', (req, res) => {
  const stream = renderToPipeableStream(<App />, {
    onShellReady() {
      res.setHeader('Content-type', 'text/html');
      stream.pipe(res);
    },
  });
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Server Components

Another major addition to React 18 is Server Components. Server Components enable developers to build apps that leverage both the server and the client for rendering, resulting in faster load times and reduced bundle sizes.

Server Components allow parts of the UI to be rendered on the server and sent to the client as HTML. This can significantly reduce the amount of JavaScript that needs to be loaded and executed on the client, leading to faster initial renders and improved performance.

// MyComponent.server.js
export default function MyComponent() {
  return <div>This is a server component</div>;
}

// App.client.js
import React, { Suspense } from 'react';
import MyComponent from './MyComponent.server';

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

export default App;

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Conclusion
React 18 is packed with features that enhance performance, improve the developer experience, and open up new possibilities for building modern web applications. Concurrent Rendering, Automatic Batching, enhanced Suspense, Transitions, improved SSR, and Server Components are just a few of the exciting additions.

As developers, these new tools and improvements allow us to build more responsive, efficient, and user-friendly applications. With React 18, the future of web development looks brighter than ever.

Stay tuned to Shanthi's Dev Diary series for more in-depth tutorials and insights into the latest in web development!