React 18 introduces an exciting new feature: Concurrent Rendering. This article takes a deep dive into what Concurrent Rendering is, its benefits, and how it represents a significant shift from the traditional synchronous rendering approach in React.

Introduction

Concurrent Rendering is a powerful feature in React 18 that allows for multiple rendering tasks to happen without blocking the user interface. This marks a significant improvement in the way React handles rendering, leading to smoother user experiences and better application performance.

What is Concurrent Rendering?

Concurrent Rendering in React 18 enables the rendering of multiple elements in the background, at their own pace, without blocking the main thread. This means React can prepare new views in the background, interrupt rendering if higher-priority updates come in, and efficiently update the UI.

Benefits of Concurrent Rendering

1. Improved User Experience: By reducing the time spent on blocking the main thread, Concurrent Rendering ensures smoother interactions.
2. Enhanced Performance: It enables React to work on high-priority updates first, improving the perceived performance of your application.
3. Flexibility in Rendering: Developers have more control over the rendering process, allowing for optimizations based on user interactions and device capabilities.

Synchronous vs. Concurrent Rendering

In traditional synchronous rendering, React processes updates in a single, uninterrupted, blocking UI thread. This can lead to jankiness and unresponsive UI during complex updates. Concurrent Rendering, on the other hand, breaks this pattern by allowing non-urgent updates to be interrupted and resumed, leading to a smoother UI experience.

Practical Examples

Using Suspense with Concurrent Rendering

React 18 expands the capabilities of Suspense, making it a great tool to use with Concurrent Rendering.

const ProfilePage = () => {
  return (
    <React.Suspense fallback={<Spinner />}>
      <UserProfile />
    </React.Suspense>
  );
};

In this example, Suspense works with Concurrent Rendering to load the UserProfile component. If it’s not ready, the Spinner is shown as a fallback.

Prioritizing Updates with useTransition

React 18 introduces a new hook called useTransition that allows developers to prioritize updates. This is useful when you want to ensure that a high-priority update is rendered before a low-priority one.

const [isPending, startTransition] = useTransition();
const [mode, setMode] = useState('edit');

const updateProfile = () => {
  startTransition(() => {
    setMode('view');
  });
};

In this example, the startTransition is used to mark the profile update as a lower priority, allowing more urgent updates to take precedence.

Conclusion

Concurrent Rendering in React 18 is a game-changer, particularly for complex applications that require a high degree of interactivity. By understanding and leveraging this feature, developers can significantly enhance the performance and user experience of their React applications.

References

• useTransition
• Suspense
• Concurrent Rendering