Concurrent Mode is a feature introduced in React that allows applications to remain responsive and interactive even when performing expensive rendering tasks. Time-slicing is a key concept in Concurrent Mode that enables React to break down large rendering tasks into smaller, incremental units, allowing it to prioritize updates and maintain a smooth user experience. In this article, we’ll delve into the concept of time-slicing, its importance, and how it works in Concurrent Mode.

What is Time-Slicing?

Time-slicing is a technique used in Concurrent Mode to divide the work of rendering and updating components into smaller chunks or slices. Instead of attempting to complete an entire rendering task in one go, React breaks it down into smaller units of work and schedules them to be executed over multiple frames. This allows React to prioritize rendering updates based on their urgency and the available resources, ensuring that the application remains responsive to user interactions.

Importance of Time-Slicing

• Improved Responsiveness: Breaking rendering tasks into smaller chunks ensures that the application remains responsive, avoiding freezes during rendering.
• Reduced Jank: Large rendering tasks can cause UI stuttering, especially on low-powered devices. Time-slicing spreads rendering work over multiple frames, reducing jank.
• Prioritized Updates: Time-slicing allows React to prioritize critical rendering updates for interactivity or visual changes, ensuring smoother user experiences.
• Optimal Resource Utilization: By dynamically adjusting rendering task scheduling based on available resources, time-slicing optimizes CPU and memory usage, even in resource-constrained environments.

How Time-Slicing Works

• Work Scheduling: React identifies rendering tasks and breaks them into smaller units called fibers. Each fiber represents a discrete unit of work that can be scheduled independently.
• Priority Assignment: React assigns priorities to fibers based on their importance. Higher-priority fibers, like user interactions or visual changes, are scheduled sooner.
• Incremental Rendering: React schedules fibers in batches or slices, allowing interruptions for other tasks like user input or animations. This incremental approach maintains application responsiveness.
• Time Budgeting: React allocates a time budget for each rendering frame. It determines how many fibers can be processed within the budget and adjusts scheduling to avoid frame drops or jank.
• Yield and Resumption: If a task exceeds the time budget, React yields control to the browser for other tasks. Once ready, it resumes rendering from where it left off, ensuring smooth progress.

Example: Implementation to show concept of time-slicing in Concurrent Mode.

// Filename - App.js

import React, { useState, useEffect } from 'react';
import ReactDOM from 'react-dom';

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

    useEffect(() => {
        const interval = setInterval(() => {
            setCount((prevCount) => prevCount + 1);
            // Increase count every second
        }, 1000);

        return () => clearInterval(interval);
    }, []);

    return (
        <div>
            <h1>Count: {count}</h1>
            <p>
                This example demonstrates
                time-slicing in Concurrent Mode.
            </p>
        </div>
    );
}

export default App;

Output:

Observing Improved Performance

With time-slicing enabled, you’ll notice smoother UI interactions, especially when dealing with large datasets or computationally intensive components. Users experience fewer delays and UI freezes, leading to a more pleasant browsing experience.

Conclusion

Time-slicing is a fundamental concept in Concurrent Mode that enables React to prioritize rendering updates, maintain responsiveness, and optimize performance in web applications. By breaking down rendering tasks into smaller units of work and scheduling them dynamically based on priorities and available resources, time-slicing ensures that the user experience remains smooth and uninterrupted, even during periods of high rendering load. As React continues to evolve, time-slicing will play an increasingly important role in enabling the development of highly responsive and interactive web applications.