React Window Tutorial: Efficient Virtualized Lists & Performance

React Window is the lightweight library for React window virtualization that makes rendering large lists fast and memory-efficient. If you're building a high-performance React list component or optimizing scroll rendering in a data-heavy UI, react-window gives you a minimal API (FixedSizeList, VariableSizeList) to render only visible items.

This tutorial covers installation, core APIs, concrete examples (including infinite scroll), and practical tips for React scroll performance and React performance optimization. It’s a focused, hands-on guide—no fluff, just the patterns you'll use in production.

Why use react-window for large lists

Rendering thousands of DOM nodes in React kills frame rates and memory. React window virtualization solves this by only mounting the small subset of items visible in the viewport. That reduces paint cost and React reconciliation work, improving scroll performance and perceived responsiveness.

Compared with heavier libraries, react-window focuses on minimalism and speed. For typical use cases—lists, grids, tables—you get FixedSizeList or VariableSizeList with straightforward API surface and predictable performance characteristics for React large list rendering.

Using react-window is not just about fewer DOM nodes; it enables better CPU and memory use, simplifies lazy-loading data, and pairs well with memoization and shouldComponentUpdate/useMemo patterns for further React performance optimization.

Installation and setup

To get started, install react-window via npm or Yarn. This is the base react-window installation step used in most getting-started guides:

npm install react-window
# or
yarn add react-window

Then import the component you need. For fixed-height rows use FixedSizeList; for variable heights use VariableSizeList. Example import:

import { FixedSizeList, VariableSizeList } from 'react-window';

If you want a guided walkthrough, check this practical getting-started tutorial "getting started with react-window" for an end-to-end example and explanations.

getting started with react-window

Core APIs: FixedSizeList and VariableSizeList

FixedSizeList is the simplest and fastest option when every row has the same height. Provide height, width, itemCount and itemSize, and render each item with the provided index. It’s the go-to for uniform lists and grids.

<FixedSizeList
  height={600}
  itemCount={10000}
  itemSize={50}
  width={'100%'}
>
  {({ index, style }) => (
    <div style={style}>Item {index}</div>
  )}
</FixedSizeList>

VariableSizeList is for lists with non-uniform heights. You must supply an itemSize function (or array) and often measure dynamic content to provide accurate sizes. VariableSizeList trades some complexity for flexibility; use it when visual variability is unavoidable.

Both components expose useful props like overscanCount to render extra off-screen items for smoother scrolling, itemKey to ensure stable keys, and onItemsRendered to coordinate data loading or virtualization-aware logic (e.g., infinite scroll).

Infinite scroll and advanced patterns

Implementing infinite scroll with react-window typically uses the onItemsRendered callback (or itemRangeRenderer patterns) to detect proximity to the end and trigger data fetches. This pattern allows you to maintain a small DOM footprint while streaming data into your list.

A basic infinite scroll pattern with FixedSizeList looks like this: subscribe to onItemsRendered, detect when visibleStopIndex is within N items of itemCount, then fetch more data and update itemCount. Pair it with a loading indicator row to show progress while fetching.

For React scroll performance, prioritize these practices: memoize row renderers, avoid inline function re-creations inside every render, minimize deep prop objects, and keep keys stable. Use overscanCount carefully (higher overscan can smooth jank at the cost of more DOM).

• Memoize row components with React.memo
• Use itemKey to prevent unnecessary re-mounts
• Limit re-renders by lifting state out of row components

If you need to mix virtualization with dynamic measurement (e.g., images of unknown height), consider measuring offscreen or using a size map. For extreme cases, combine react-window with a sizing solution that reports heights to a VariableSizeList.

Examples: practical code patterns

Fixed-size example (simple list):

function Row({ index, style }) {
  return <div style={style}>Row {index}</div>
}

<FixedSizeList
  height={500}
  itemCount={100000}
  itemSize={35}
  width={300}
>
  {Row}
</FixedSizeList>

Infinite loader pattern using onItemsRendered:

function onItemsRendered({ visibleStopIndex }) {
  if (visibleStopIndex >= items.length - 10 && !isLoading) {
    loadMore(); // fetch next page and append to items
  }
}

Variable heights example requires an itemSize getter. Maintain a map of measured heights and update the list's itemSize when measurements change to avoid layout drift. Measure once per item and cache results for performance.

Semantic core (keywords and clusters)

Use this semantic core to guide metadata, internal linking, and on-page keyword usage. Grouped by intent:

• Primary: react-window, react-window tutorial, react-window installation, react-window getting started, React window virtualization
• Secondary: react-window FixedSizeList, react-window VariableSizeList, React virtualized list, React large list rendering, React list component
• Clarifying / long tail: react-window example, react-window setup, React performance optimization, React scroll performance, React infinite scroll, react-window installation command

Backlinks & further reading

Official repo and docs for the library live on GitHub and are essential reference material. See the react-window GitHub for API details and examples.

For a step-by-step walk-through, the guide getting started with react-window provides a hands-on react-window tutorial and real-world examples you can clone and run.

FAQ

How do I install and get started with react-window?

Install with npm or Yarn: npm install react-window or yarn add react-window. Import FixedSizeList or VariableSizeList, provide height, width, itemCount and itemSize (or itemSize getter) and render your row function. Use onItemsRendered for infinite loading.

When should I use FixedSizeList vs VariableSizeList?

Use FixedSizeList when all rows have the same height—it's simpler and faster. Use VariableSizeList when items vary in height; it requires you to supply or measure sizes, which adds complexity and some performance overhead.

How can I implement infinite scroll with react-window?

Listen to onItemsRendered and detect when the visibleStopIndex approaches itemCount. Trigger a fetch for the next page, append items to state, and update itemCount. Optionally render a loading row while data arrives. Debounce or guard the fetch to avoid duplicate requests.

Tip: For production-grade infinite loading, combine react-window with a request queue and stable keys to avoid flicker.