@shopify/flash-list/README.md

FlashList is a more performant FlatList replacement

![FlashList Image](./FlashList.png)

<div align="center">
  <a href="https://shopify.github.io/flash-list/">Website</a> •
  <a href="https://discord.gg/k2gzABTfav">Discord</a> •
  <a href="https://shopify.github.io/flash-list/docs/">Getting started</a> •
  <a href="https://shopify.github.io/flash-list/docs/usage">Usage</a> •
  <a href="https://shopify.github.io/flash-list/docs/performance-troubleshooting">Performance</a> •
  <a href="https://shopify.github.io/flash-list/docs/fundamentals/performant-components">Writing performant components</a> •
  <a href="https://shopify.github.io/flash-list/docs/known-issues">Known Issues</a>
<br><br>

**Fast & performant React Native list. No more blank cells.**

Swap from FlatList in seconds. Get instant performance.

</div>

## React Native's new architecture support

FlashList is compatible with React Native's new architecture however, it's not fully optimized for it yet. You will still gain performance benefits from using FlashList over FlatList. Stayed tuned for more improvements.

## Installation

Add the package to your project via `yarn add @shopify/flash-list` and run `pod install` in the `ios` directory.

## Usage

We recommend reading the detailed documentation for using `FlashList` [here](https://shopify.github.io/flash-list/docs/usage).

But if you are familiar with [FlatList](https://reactnative.dev/docs/flatlist), you already know how to use `FlashList`. You can try out `FlashList` by changing the component name and adding the `estimatedItemSize` prop or refer to the example below:

```jsx
import React from "react";
import { View, Text } from "react-native";
import { FlashList } from "@shopify/flash-list";

const DATA = [
  {
    title: "First Item",
  },
  {
    title: "Second Item",
  },
];

const MyList = () => {
  return (
    <FlashList
      data={DATA}
      renderItem={({ item }) => <Text>{item.title}</Text>}
      estimatedItemSize={200}
    />
  );
};
```

To avoid common pitfalls, you can also follow these steps for migrating from `FlatList`, based on our own experiences:

1. Switch from `FlatList` to `FlashList` and render the list once. You should see a warning about missing `estimatedItemSize` and a suggestion. Set this value as the prop directly.
2. **Important**: Scan your [`renderItem`](https://shopify.github.io/flash-list/docs/usage/#renderitem) hierarchy for explicit `key` prop definitions and remove them. If you’re doing a `.map()` use indices as keys.
3. Check your [`renderItem`](https://shopify.github.io/flash-list/docs/usage/#renderitem) hierarchy for components that make use of `useState` and verify whether that state would need to be reset if a different item is passed to that component (see [Recycling](https://shopify.github.io/flash-list/docs/recycling))
4. If your list has heterogenous views, pass their types to `FlashList` using [`getItemType`](https://shopify.github.io/flash-list/docs/usage/#getitemtype) prop to improve performance.
5. Do not test performance with JS dev mode on. Make sure you’re in release mode. `FlashList` can appear slower while in dev mode due to a small render buffer.

## App / Playground

The [fixture](https://github.com/Shopify/flash-list/tree/main/fixture) is an example app showing how to use the library.