Understanding Concurrent Rendering in React: Why We Need It and How to Utilize It

React has consistently evolved to meet the demands of modern web development, with React 18 introducing one of its most significant features: Concurrent Rendering. This feature enhances the performance and user experience of React applications by allowing multiple UI updates to be processed simultaneously. In this article, we’ll explore what Concurrent Rendering is, why it’s necessary, the problems it solves, and how developers can utilize it effectively.

What is Concurrent Rendering?

Concurrent Rendering is a new capability in React that allows the library to work on multiple tasks simultaneously without blocking the main thread. This means React can prepare multiple versions of the UI at the same time, prioritizing more critical updates like user interactions over less urgent ones.

Key Concept

In traditional rendering, React processes updates sequentially, which can sometimes lead to performance bottlenecks, especially in complex applications with heavy computational loads. Concurrent Rendering, on the other hand, enables React to interrupt less important tasks to handle more urgent updates first, resulting in a smoother and more responsive user experience.

Why Do We Need Concurrent Rendering?

The primary goal of Concurrent Rendering is to improve the responsiveness of React applications. Here are some specific reasons why it’s necessary:

1. Improved User Experience: By allowing high-priority updates (such as user inputs) to be processed without delay, applications feel faster and more responsive to users.
2. Efficient Resource Utilization: Concurrent Rendering makes better use of the available resources by distributing tasks more effectively, ensuring that no single task monopolizes the main thread.
3. Reduced Latency: By prioritizing critical updates, the perceived latency of the application decreases, making interactions smoother.
4. Enhanced Performance in Complex UIs: Applications with complex UIs and heavy computations benefit significantly as React can manage and optimize the rendering process more intelligently.

Problems Solved by Concurrent Rendering

1. Blocking Updates

In traditional rendering, long-running tasks can block the main thread, causing the UI to freeze and become unresponsive. Concurrent Rendering mitigates this issue by allowing React to interrupt these tasks to handle more critical updates.

2. Janky Animations

Animations and transitions can appear janky or stutter if the main thread is busy with other tasks. Concurrent Rendering helps by ensuring that animations are prioritized and run smoothly without interruptions.

3. Slow Response to User Input

User inputs such as typing, clicking, or scrolling can feel sluggish if React is busy processing other updates. Concurrent Rendering ensures these inputs are handled promptly, enhancing the overall user experience.

How to Utilize Concurrent Rendering

React 18 introduced several new hooks and APIs to leverage Concurrent Rendering effectively. Here’s how you can utilize these features in your application:

1. Enabling Concurrent Mode

To use Concurrent Rendering, you need to enable Concurrent Mode in your application. This can be done by using the createRoot API instead of the ReactDOM.render method.

import { createRoot } from 'react-dom/client';
import App from './App';
const rootElement = document.getElementById('root');
const root = createRoot(rootElement);
root.render(<App />);

2. Using the useTransition Hook

The useTransition hook allows you to mark updates as transitions, which are less urgent and can be deferred to improve performance.

import React, { useState, useTransition } from 'react';
function App() {
  const [isPending, startTransition] = useTransition();
  const [value, setValue] = useState('');
  const handleChange = (e) => {
    startTransition(() => {
      setValue(e.target.value);
    });
  };
  return (
<div>
      <input type="text" onChange={handleChange} />
      {isPending && 
Updating...
}
{value}
</div>
  );
}

3. Using the useDeferredValue Hook

The useDeferredValue hook allows you to defer updates to a value, improving the performance of the application by allowing non-critical updates to be processed later.

import React, { useState, useDeferredValue } from 'react';
function App() {
  const [value, setValue] = useState('');
  const deferredValue = useDeferredValue(value);
  return (
<div>
      <input type="text" onChange={(e) => setValue(e.target.value)} />
{deferredValue}
</div>
  );
}

4. Using Suspense for Data Fetching

Concurrent Rendering enhances the Suspense component, allowing for better handling of asynchronous data fetching and loading states.

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 in React 18 marks a significant step forward in building responsive and performant web applications. By enabling React to handle multiple tasks simultaneously and prioritize critical updates, developers can ensure their applications remain fast and responsive under heavy load. Utilizing Concurrent Rendering features like useTransition, useDeferredValue, and Suspense allows for a smoother and more efficient user experience, making it a crucial tool in any React developer’s toolkit.