React Concurrent Mode


What is Concurrent Mode in React?

In React, Concurrent Mode is a powerful feature introduced in version 18. It allows developers to build components that render concurrently—meaning they can render simultaneously without blocking the user interface. Imagine having the superpower to enhance your application’s performance by rendering components in a non-blocking manner!

Here are the key points about Concurrent Mode:

  1. Time Slicing Algorithm: The magic behind Concurrent Mode lies in the Time Slicing algorithm. React breaks down rendering into smaller, prioritized chunks called fiber nodes. These nodes are scheduled based on priority and expiration time. The highest-priority fiber nodes (like buttons and menus) are updated quickly, while lower-priority nodes (such as hidden tabs or off-screen parts) are processed later. This ensures a smooth user experience even during rendering.

  2. Asynchronous Updates: Concurrent Mode introduces new APIs for rendering scheduling and managing asynchronous updates. These APIs, such as unstable_scheduleCallback and unstable_cancelCallback, allow developers to control rendering priorities and postpone updates until they are ready. This further improves performance.

import React, { unstable_ConcurrentMode as ConcurrentMode } from 'react';

function App() {
return (
<h1>Hello, world!</h1>

export default App;

3. Benefits of Concurrent Mode:

  • Improved Performance: By rendering components concurrently, your application becomes more responsive, allowing users to interact without delays.

  • Prioritized Updates: You can prioritize which parts of the component tree need updates, ensuring critical UI elements are handled promptly.

  • Controlled Asynchrony: Asynchronous updates give you fine-grained control over rendering, making your app more efficient.


While Concurrent Mode brings significant benefits, it’s essential to be aware of potential challenges. These include managing state correctly, handling side effects, and ensuring compatibility with existing code.

In summary, React’s Concurrent Mode revolutionizes UI performance by allowing seamless rendering, prioritization, and asynchronous updates. As a modern web developer, understanding and utilizing Concurrent Mode can elevate your application’s user experience. 🌟