React Concurrent Mode | Advanced Concepts

Introduction to React Concurrent Mode

React Concurrent Mode is a set of new features that help React apps stay responsive and gracefully adjust to the user's device capabilities and network speed. Concurrent Mode allows React to work on multiple tasks at the same time and prioritize urgent tasks, ensuring a smooth and responsive user experience. This tutorial covers the key concepts and usage of React Concurrent Mode.

Key Points:

React Concurrent Mode helps apps stay responsive by prioritizing urgent tasks.
It allows React to work on multiple tasks simultaneously.
Concurrent Mode improves user experience by making React apps feel more responsive and fluid.

Enabling Concurrent Mode

To use Concurrent Mode in your React application, you need to enable it in your root render method. Concurrent Mode is still experimental, so you need to use ReactDOM.createRoot instead of ReactDOM.render:


// index.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

ReactDOM.createRoot(document.getElementById('root')).render(<App />);

Using `Suspense` with Concurrent Mode

Concurrent Mode works seamlessly with Suspense, allowing you to manage asynchronous operations and show fallback content while loading data:


// Data fetching function
const fetchData = () => {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve('Data fetched!');
        }, 2000);
    });
};

// Creating a resource
const createResource = (promise) => {
    let status = 'pending';
    let result;
    let suspender = promise.then(
        (res) => {
            status = 'success';
            result = res;
        },
        (err) => {
            status = 'error';
            result = err;
        }
    );
    return {
        read() {
            if (status === 'pending') {
                throw suspender;
            } else if (status === 'error') {
                throw result;
            } else if (status === 'success') {
                return result;
            }
        },
    };
};

const resource = createResource(fetchData());

// Component using Suspense
import React, { Suspense } from 'react';

const DataComponent = () => {
    const data = resource.read();
    return <div>{data}</div>;
};

const App = () => {
    return (
        <div>
            <h1>React Concurrent Mode Demo</h1>
            <Suspense fallback="Loading...">
                <DataComponent />
            </Suspense>
        </div>
    );
};

export default App;

Using `useTransition` and `useDeferredValue`

React provides two hooks, useTransition and useDeferredValue, to help manage transitions and deferred updates:


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

const App = () => {
    const [isPending, startTransition] = useTransition();
    const [count, setCount] = useState(0);

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

    return (
        <div>
            <button onClick={handleClick}>Increment</button>
            {isPending ? 'Loading...' : <p>Count: {count}</p>}
        </div>
    );
};

export default App;

// Using useDeferredValue
import React, { useState, useDeferredValue } from 'react';

const App = () => {
    const [input, setInput] = useState('');
    const deferredInput = useDeferredValue(input);

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

    return (
        <div>
            <input type="text" value={input} onChange={handleChange} />
            <p>Deferred Input: {deferredInput}</p>
        </div>
    );
};

export default App;

Best Practices

Here are some best practices for using React Concurrent Mode in your applications:

Use Suspense for managing asynchronous operations and showing fallback content.
Leverage useTransition for managing state transitions and keeping the UI responsive.
Utilize useDeferredValue to defer non-urgent updates and improve performance.
Test your application thoroughly to ensure that it works correctly with Concurrent Mode.
Keep an eye on the React documentation for updates and best practices as Concurrent Mode evolves.

Summary

In this tutorial, you learned about React Concurrent Mode, which helps React apps stay responsive and gracefully adjust to the user's device capabilities and network speed. Concurrent Mode allows React to work on multiple tasks at the same time and prioritize urgent tasks, improving the user experience. By enabling Concurrent Mode, using Suspense, useTransition, and useDeferredValue, and following best practices, you can build more responsive and fluid React applications.

React - React Concurrent Mode