Last updated at 2023-09-11

Performance Improvement with react-window FixedSizeList in React.js

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Sep 11, 2023 09:53 AM
Sep 11, 2023


When building complex web applications with React, optimizing performance is crucial for delivering a smooth user experience.
One common performance bottleneck in web applications is rendering long lists of items.
Fortunately, React offers a solution in the form of the react-window library, specifically the FixedSizeList component.
In this article, we'll explore how to use FixedSizeList to dramatically improve the performance of rendering long lists in your React applications.

The Problem: Inefficient Rendering of Long Lists

Before diving into the solution, let's understand the problem.
In a typical React application, rendering a long list of items can lead to performance issues, especially on mobile devices or lower-end hardware.
This happens because React renders all the list items, even if they are not currently visible on the screen.
This unnecessary rendering consumes memory and CPU cycles, resulting in sluggish user interfaces.

Enter react-window and FixedSizeList

react-window is a library designed to tackle this problem head-on. It provides a suite of tools for efficiently rendering large lists and grids in React applications.
One of its most popular components is FixedSizeList.
FixedSizeList is designed for rendering a fixed number of items at a time, and it only renders the items that are currently visible within the viewport.
This approach greatly reduces the amount of work that React has to do, resulting in significantly improved performance.

Using FixedSizeList

Here's how you can use FixedSizeList in your React project:

1. Installation

First, install the react-window library:
npm install react-window

2. Importing

Import FixedSizeList into your component:
import { FixedSizeList } from 'react-window';

3. Create a FixedSizeList

Use FixedSizeList in your component, providing it with the necessary props:
const MyListComponent = ({ items }) => { const itemCount = items.length; const itemSize = 50; // Height of each item in pixels const renderItem = ({ index, style }) => ( <div style={style}>{items[index]}</div> ); return ( <FixedSizeList height={400} // Height of the list in pixels width={300} // Width of the list in pixels itemCount={itemCount} itemSize={itemSize} > {renderItem} </FixedSizeList> ); };

4. Enjoy Improved Performance

With FixedSizeList, you've effectively optimized your list rendering.
Only the items that are currently in view will be rendered, making your application more performant, especially with long lists.

Additional Benefits

  • Accessibility: react-window automatically handles accessibility concerns, ensuring that screen readers can navigate the list seamlessly.
  • Dynamic Item Sizes: While we used a fixed item size in this example, FixedSizeList can also handle lists with dynamic item heights.
  • Customization: You can customize the appearance and behavior of your list using various props and callbacks.


Efficiently rendering long lists is a common challenge in React applications.
react-window's FixedSizeList offers an elegant solution that significantly boosts performance by only rendering the items currently visible in the viewport. By incorporating react-window into your projects, you can create smooth and responsive user interfaces, enhancing the overall user experience. So, the next time you're faced with a lengthy list of data to display, remember to reach for FixedSizeList and take your React app's performance to the next level. Happy coding!

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