react-native-swc

SWC-powered transformer for Metro

• 🔧 Drop-in replacement for Metro Babel transform worker and minifier
• 🦀 All transformation in Rust, no Babel in sight
• 🏎️ Fast: transform worker is ~8× faster & full real world bundling ~3× faster
• ⚡️ Battery friendly: 15× less CPU utilization
• 🚇 Feature parity with Metro: HMR, inline requires, Platform.select() substituion, constant folding, delta bundles etc
• 🔤 Native support for Flow, TypeScript, ESM, CJS, JSX
• 🧵 Worklet/Reanimated support without Babel through custom SWC plugin
• 🔌 Support for SWC plugins and process.env inlining
• ⚛️ Expo Plugin for seamless integration

Install

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yarn add -D @react-native-swc/core

If your app uses react-native-reanimated:

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yarn add -D @react-native-swc/worklets-plugin

Setup

Expo (managed / CNG) — config plugin

Add @react-native-swc/core to app.json:

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{
  "expo": {
    "plugins": ["@react-native-swc/core"]
  }
}

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npx expo prebuild

The plugin writes (or updates) a metro.config.js wired up to withSwcTransformer. If react-native-worklets is listed in your dependencies, the worklets SWC plugin is registered automatically. Any EXPO_PUBLIC_* env vars present at metro start are inlined into the bundle, matching Expo's default Babel pipeline. If you already have a manual withSwcTransformer call, the plugin leaves your config alone.

Disable worklet auto-detection if needed:

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["@react-native-swc/core", { "worklets": false }]

Note. Expo config plugins run only during expo prebuild (and eas build, which invokes prebuild). Running expo start alone does not re-run plugins.

Bare React Native / Expo (manual)

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// metro.config.js
const { getDefaultConfig, mergeConfig } = require('@react-native/metro-config');
const { withSwcTransformer } = require('@react-native-swc/core');

module.exports = withSwcTransformer(mergeConfig(getDefaultConfig(__dirname), {}));

For Expo without the config plugin, swap @react-native/metro-config for expo/metro-config. To match Expo's default EXPO_PUBLIC_* env-var inlining, forward those vars through swcConfig.envs:

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// metro.config.js
const { getDefaultConfig } = require('expo/metro-config');
const { withSwcTransformer } = require('@react-native-swc/core');

/** @type {import('@react-native-swc/core').SwcTransformerOptions} */
const swcConfig = {
  envs: Object.fromEntries(
    Object.entries(process.env).filter(([k, v]) => k.startsWith('EXPO_PUBLIC_')),
  ),
};

module.exports = withSwcTransformer(getDefaultConfig(__dirname), swcConfig);

process.env.EXPO_PUBLIC_FOO references in your source are then replaced with the literal value at bundle time. Anything not prefixed with EXPO_PUBLIC_ is left alone.

Worklets (react-native-reanimated) — manual

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// metro.config.js
const { getDefaultConfig } = require('@react-native/metro-config');
const { withSwcTransformer } = require('@react-native-swc/core');

/** @type {import('@react-native-swc/core').SwcTransformerOptions} */
const swcConfig = {
  plugins: [
    [
      '@react-native-swc/worklets-plugin',
      {
        pluginVersion: require('react-native-worklets/package.json').version,
      },
    ],
  ],
};

module.exports = withSwcTransformer(getDefaultConfig(__dirname), swcConfig);

Configuration

withSwcTransformer(metroConfig, swcOptions?) exposes an intentionally narrow surface — everything that affects Metro correctness is owned by the transform worker:

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interface SwcTransformerOptions {
  plugins?: ReadonlyArray<[string, Record<string, unknown>]>;
  /**
   * `process.env.FOO`-style replacements to inline at build time. Values are
   * JSON-encoded for you and merged with the worker's built-ins (`NODE_ENV`,
   * `EXPO_OS`, …). E.g. `{ API_URL: "https://x" }` replaces
   * `process.env.API_URL` with the literal string `"https://x"`.
   */
  envs?: Record<string, string>;
}

Limitations

• Custom Babel plugins from babel.config.js are not executed. Reanimated is covered by @react-native-swc/worklets-plugin in this repo, for other use cases see SWC plugin directory.
• TypeScript sources must be isolatedModules-compatible. SWC parses each file in isolation.
• Flow handling is automatic. User .js files are parsed as Flow only if they carry an @flow / @noflow pragma or if they first fail to parse as plain JavaScript.

Contributing

See CONTRIBUTING.md.

License

MIT.