Exploring the New React Features in Concurrent Mode
React's Concurrent Mode is a groundbreaking set of features designed to improve the performance and responsiveness of applications by enabling React to interrupt and prioritize rendering tasks. By allowing React to work on multiple tasks simultaneously, Concurrent Mode aims to make user interfaces smoother and more responsive. This article will explore the new features introduced with Concurrent Mode, how they work, and how to use them effectively in your React applications.
M Zeeshan
8/16/20243 min read
What is Concurrent Mode?
Concurrent Mode is a set of experimental features in React that help manage rendering more efficiently by enabling:
Interruptible Rendering: React can pause, resume, or discard rendering work to keep the interface responsive.
Prioritized Updates: React can prioritize updates based on their importance, ensuring that crucial updates (like user interactions) are handled promptly.
Background Rendering: React can prepare updates in the background, reducing the time users wait for updates to appear on screen.
Key Features of Concurrent Mode
1. Suspense for Data Fetching
Suspense was initially introduced to handle code splitting but has been extended to support data fetching. With Concurrent Mode, you can use Suspense to manage loading states for asynchronous data.
How It Works:
Wrap components that fetch data with React.Suspense.
Provide a fallback UI that displays while the data is loading.
Example:
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import React, { Suspense, lazy } from 'react'; const UserProfile = lazy(() => import('./UserProfile')); function App() { return ( <div> <Suspense fallback={<div>Loading...</div>}> <UserProfile /> </Suspense> </div> ); } export default App;
In this example, UserProfile is loaded asynchronously, and the fallback UI is displayed while it's loading.
2. Concurrent Rendering
Concurrent Rendering enables React to work on multiple tasks simultaneously. It helps to keep the UI responsive by pausing and resuming rendering tasks based on priority.
How It Works:
React can interrupt rendering work to prioritize user interactions or critical updates.
React schedules updates based on their priority, ensuring that high-priority tasks are handled first.
Example:
React automatically applies concurrent rendering, so there's no need for special syntax. However, using concurrent features like Suspense and useTransition helps to leverage this capability.
3. useTransition Hook
The useTransition hook allows you to mark certain state updates as non-urgent, helping React prioritize them accordingly.
How It Works:
Wrap state updates with startTransition to mark them as low-priority.
React will keep the interface responsive by deferring these updates when needed.
Example:
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import React, { useState, useTransition } from 'react'; function App() { const [isPending, startTransition] = useTransition(); const [inputValue, setInputValue] = useState(''); const handleChange = (e) => { startTransition(() => { setInputValue(e.target.value); }); }; return ( <div> <input type="text" onChange={handleChange} /> {isPending && <div>Loading...</div>} <p>Input value: {inputValue}</p> </div> ); } export default App;
In this example, handleChange uses startTransition to ensure that input updates are low-priority, keeping the UI responsive.
4. useDeferredValue Hook
The useDeferredValue hook allows you to defer updates to a piece of state, making it easier to manage rendering performance for less critical updates.
How It Works:
Use useDeferredValue to get a deferred version of the state that updates at a lower priority.
This helps to keep the interface responsive by deferring non-critical updates.
Example:
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import React, { useState, useDeferredValue } from 'react'; function App() { const [inputValue, setInputValue] = useState(''); const deferredValue = useDeferredValue(inputValue); return ( <div> <input type="text" onChange={(e) => setInputValue(e.target.value)} /> <p>Input value: {inputValue}</p> <p>Deferred value: {deferredValue}</p> </div> ); } export default App;
In this example, deferredValue is updated with a slight delay, allowing the UI to remain responsive while the input value is updated.
5. Concurrent Mode and Suspense for Transitions
Concurrent Mode enhances Suspense by enabling smooth transitions between different states of your application.
How It Works:
Use Suspense and useTransition together to manage transitions smoothly.
Concurrent Mode helps to manage these transitions in the background, making the UI more responsive.
Example:
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import React, { useState, useTransition, Suspense, lazy } from 'react'; const Details = lazy(() => import('./Details')); function App() { const [showDetails, setShowDetails] = useState(false); const [isPending, startTransition] = useTransition(); return ( <div> <button onClick={() => startTransition(() => setShowDetails(!showDetails))}> Toggle Details </button> {isPending && <div>Loading...</div>} <Suspense fallback={<div>Loading...</div>}> {showDetails && <Details />} </Suspense> </div> ); } export default App;
This example shows how to use Suspense with useTransition to handle transitions between different UI states smoothly.
How to Enable Concurrent Mode
To enable Concurrent Mode, you need to wrap your entire application with the <ConcurrentMode> component. This is an experimental feature and requires specific setup.
Example:
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import React from 'react'; import ReactDOM from 'react-dom'; import App from './App'; ReactDOM.createRoot(document.getElementById('root')).render( <React.StrictMode> <App /> </React.StrictMode> );
Currently, Concurrent Mode is available as an experimental feature in React 18 and can be enabled using the createRoot API.
Conclusion
Concurrent Mode is a significant advancement in React, offering improved performance and responsiveness by enabling interruptible and prioritized rendering. By using features like Suspense, useTransition, and useDeferredValue, you can create more fluid and responsive user interfaces. Although Concurrent Mode is still experimental, it provides powerful tools for handling complex rendering scenarios and can greatly enhance the user experience in your React applications.
As React continues to evolve, staying up-to-date with Concurrent Mode and other new features will help you build more efficient and engaging applications.