Expo Docs MCP Server

--- title: React Compiler description: Learn how to enable and use the React Compiler in Expo apps. --- > **warning** **Warning:** React Compiler is experimental. Currently, it is on hold and we'll soon provide more updates on its usage. The new [React Compiler](https://react.dev/learn/react-compiler) automatically memoizes components and hooks to enable fine-grained reactivity. This can lead to significant performance improvements in your app. The React Compiler is currently experimental and is not enabled by default. You can enable it in your app by following the instructions below. ## Enabling React Compiler [Check how compatible](https://react.dev/learn/react-compiler#checking-compatibility) your project is with the React Compiler. This will generally verify if your app is following the [**rules of React**](https://react.dev/reference/rules). Install `babel-plugin-react-compiler` and the React compiler runtime in your project: <Tabs tabs={['SDK 54 and above', 'SDK 53', 'SDK 52 and below']}> <Tab> Babel is automatically configured in Expo SDK 54 and above. </Tab> <Tab> </Tab> <Tab> </Tab> </Tabs> Toggle on the React Compiler experiment in your app config file: ```json app.json { "expo": { "experiments": { "reactCompiler": true } } } ``` ### Enabling the linter > In the future, all of the following steps below will be automated by Expo CLI. Additionally, you should use the ESLint plugin to continuously enforce the rules of React in your project. Run [`npx expo lint`](/guides/using-eslint/#eslint) to ensure ESLint is setup in your app, then install the ESLint plugin for React Compiler: Update your [ESLint configuration](/guides/using-eslint/) to include the plugin: ```js .eslintrc.js // https://docs.expo.dev/guides/using-eslint/ const { defineConfig } = require('eslint/config'); const expoConfig = require('eslint-config-expo/flat'); module.exports = defineConfig([ expoConfig, { ignores: ['dist/*'], plugins: ['react-compiler'], rules: { 'react-compiler/react-compiler': 'error', }, }, ]); ``` ## Incremental adoption You can incrementally adopt the React Compiler in your app using a few strategies: Configure the Babel plugin to only run on specific files or components. To do this: 1. If your project doesn't have [**babel.config.js**](/versions/latest/config/babel/), create one by running `npx expo customize babel.config.js`. 2. Add the following configuration to **babel.config.js**: ```js babel.config.js module.exports = function (api) { api.cache(true); return { presets: [ [ 'babel-preset-expo', { 'react-compiler': { sources: filename => { // Match file names to include in the React Compiler. return filename.includes('src/path/to/dir'); }, }, }, ], ], }; }; ``` Whenever you change your **babel.config.js** file, you need to restart the Metro bundler to apply the changes: Use the `"use no memo"` directive to opt out of the React Compiler for specific components or files. ```jsx function MyComponent() { 'use no memo'; return <Text>Will not be optimized</Text>; } ``` ## Usage > To better understand how React Compiler works, check out the [React Playground](https://playground.react.dev/). Improvements are primarily automatic. You can remove instances of `useCallback`, `useMemo`, and `React.memo` in favor of the automatic memoization. Class components will not be optimized. Instead, migrate to function components. Expo's implementation of the React Compiler will only run on application code (no node modules), and only when bundling for the client (disabled in server rendering). ## Configuration You can pass additional settings to the React Compiler Babel plugin by using the `react-compiler` object in the Babel configuration: ```js babel.config.js module.exports = function (api) { api.cache(true); return { presets: [ [ 'babel-preset-expo', { 'react-compiler': { // Passed directly to the React Compiler Babel plugin. compilationMode: 'strict', panicThreshold: 'all_errors', }, web: { 'react-compiler': { // Web-only settings... }, }, }, ], ], }; }; ```