Step-by-Step: How to Virtualize Large Lists Using React-Window

Too many items in your React list? Speed up your app by rendering only what’s needed with React Window. Learn how to handle large lists efficiently for smoother performance and better user experience.

Rendering every item in a long list can silently drain your React app’s performance. As the list grows, so does the lag—and users feel it.

What if your app only loaded what's actually on screen?

In this blog, you'll learn how to virtualize large lists using React Window . This approach keeps your UI fast and responsive by limiting the number of elements in the DOM. We'll walk through setup, performance tweaks, and real-world use cases like infinite scrolling and tables.

Key Takeaways

• React Window helps reduce DOM nodes by rendering only visible items.

• Supports infinite scroll with react window infinite loader integration.

• Handles large data sets efficiently using fixed size lists.

• Uses lazy loading to reduce load on low end devices.

• Works well for tabular data and virtualized grid layouts.

What is List Virtualization?

List virtualization (also called windowing) is a performance technique that involves rendering only a small subset of items in a list component, depending on what’s visible to the user. When the user scrolls, new items replace the old ones in the DOM, instead of rendering the entire list.

This significantly reduces the number of DOM nodes created, improving both render speed and memory usage in modern browsers.

Why React Window?

React Window, created by Brian Vaughn (also known for React Virtualized), offers a lightweight, flexible way to virtualize large lists. It’s much faster and simpler than React Virtualized for most use cases. It’s ideal when you’re working with large data sets, fixed height rows, and need to avoid overloading the browser with unnecessary renders.

Getting Started with React Window

To begin, install the library:

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1npm install react-window

Basic Setup

Here's how to display a list of 10,000 items with React Window.

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1import React from 'react';
2import { FixedSizeList as List } from 'react-window';
3import faker from 'faker';
4
5const items = Array.from({ length: 10000 }, (_, index) => faker.name.findName());
6
7const Row = ({ index, style }) => (
8  <div style={style}>
9    Row {index}: {items[index]}
10  </div>
11);
12
13export default function App() {
14  return (
15    <List
16      height={600}
17      itemCount={items.length}
18      itemSize={35}
19      width={300}
20    >
21      {Row}
22    </List>
23  );
24}

• height: viewport height in pixels.

• itemSize: fixed height for each item.

• itemCount: total number of items.

• width: width of the list container.

You can see that only a small subset of rows is rendered based on what’s visible to the user.

How Virtualization Works

When the user scrolls, React Window calculates the current scroll position and dynamically decides which items to render.

Explanation:

• React Window monitors the scroll.

• Based on the user scrolls, it recalculates the visible parts of the list.

• The DOM nodes are updated with the new row component content.

This method avoids unnecessary dom mutations and keeps the browser snappy.

Virtualizing Tabular Data

To display tabular data, use the FixedSizeGrid component. This creates a virtualized grid that works the same way as the list.

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1import React from 'react';
2import { FixedSizeGrid as Grid } from 'react-window';
3import faker from 'faker';
4
5const columns = 5;
6const items = Array.from({ length: 1000 * columns }, () => faker.name.firstName());
7
8const Cell = ({ columnIndex, rowIndex, style }) => {
9  const index = rowIndex * columns + columnIndex;
10  return <div style={style}>{items[index]}</div>;
11};
12
13export default function App() {
14  return (
15    <Grid
16      columnCount={columns}
17      columnWidth={150}
18      height={600}
19      rowCount={1000}
20      rowHeight={35}
21      width={800}
22    >
23      {Cell}
24    </Grid>
25  );
26}

Use case: Ideal for data tables and dashboards that require a grid layout.

Adding Infinite Scroll with React Window Infinite Loader

To load more items as the user scrolls, use the react window infinite loader.

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1import React from 'react';
2import { FixedSizeList as List } from 'react-window';
3import InfiniteLoader from 'react-window-infinite-loader';
4
5const loadMore = (startIndex, stopIndex) => {
6  // Simulate API call
7  return new Promise(resolve => setTimeout(resolve, 1000));
8};
9
10const isItemLoaded = index => !!items[index];
11
12const Row = ({ index, style }) => (
13  <div style={style}>Row {index}: {items[index] || 'Loading...'}</div>
14);
15
16export default function App() {
17  return (
18    <InfiniteLoader
19      isItemLoaded={isItemLoaded}
20      itemCount={10000}
21      loadMoreItems={loadMore}
22    >
23      {({ onItemsRendered, ref }) => (
24        <List
25          height={600}
26          itemCount={10000}
27          itemSize={35}
28          onItemsRendered={onItemsRendered}
29          ref={ref}
30          width={300}
31        >
32          {Row}
33        </List>
34      )}
35    </InfiniteLoader>
36  );
37}

• InfiniteLoader integrates seamlessly with React Window

• Dynamically loads more items based on user scrolls

React Window vs React Virtualized

For most frontend developer use cases, React Window provides better performance and simplicity.

Best Practices

• Use fixed size lists when possible for better performance

• Minimize re-renders of row components

• Use lazy loading and infinite loader for very large lists

• Avoid unnecessary div className nesting

• Keep import React at the top of each file

• Export the app using export default App

Troubleshooting Performance Problems

If you're still facing performance problems:

• Profile the app with React DevTools

• Monitor render count of each component

• Verify you're only creating DOM nodes that are visible

• Avoid deep DOM node nesting

Start Improving Scroll Performance in Your React Apps Now

Virtualizing large lists with React Window solves common performance bottlenecks by rendering only what is visible to the user, minimizing DOM nodes, and avoiding unnecessary re-renders. This directly addresses challenges like slow scroll speeds, memory spikes, and poor responsiveness in React applications working with large data sets.

With the growing demand for responsive UIs and efficient rendering, especially on low end devices, using React Window has become more relevant than ever. It’s a lightweight, effective way to handle infinite scroll, display tabular data, and ensure smoother user experiences.

Start implementing React Window now to reduce performance issues and streamline your front-end workflows. Don't wait until your users feel the lag—optimize while you scale.