How do I know if the React Compiler is working?

[salieflewis]

I read in the React Native 0.78 Release Notes that "components that are memoized have the Memo ✨ tag attached to them in the Component Inspector."

I'm using Expo SDK 52 and followed the instructions here for enabling React Compiler, yet I don't see any of those Memo ✨ tags when viewing the React DevTools. Is it safe to assume that it should appear in the version of React Native that I am using (0.76.7) or is there something else I need to do to enable it?

[zaxovaiko]

I followed the exact instructions as you did, and I can't see this Memo ✨ thing. But I tried to see if actual rerenders of child components are happening, and it appears that they are not. So, I assume the setup of RC is working, but it doesn't show the memo badge on dev tools for some reason.

export default function Compiler() {
  const [count, setCount] = useState(0);

  return (
    <>
      <Button title={`Count: ${count}`} onPress={() => setCount(p => p + 1)} />
      <Random />
    </>
  );
}

const Random = () => {
  return (
      <Text>{Math.random()}</Text>
  );
};

[salieflewis]

Yeah this is so odd to me, and in my conversation with @hirbod on Twitter, he suggested that they should be. So I'm a bit confused as well.

[AndreiTS]

I recommend using this extension: https://marketplace.visualstudio.com/items?itemName=blazejkustra.react-compiler-marker

It shows if the component you are working is memoized by the compiler.

The react extension for chrome doesn't work 100%

[blazejkustra]

Thank you! 🙌

[PrithwishDas101]

The missing Memo ✨ indicator doesn't necessarily mean the React Compiler isn't working.

The important detail is that the Memo ✨ indicator in React Native DevTools was introduced in React Native 0.78. You're using 0.76.7, so you shouldn't expect that indicator to appear in your current version.

Expo SDK 52 can still enable the React Compiler through its Babel integration. To verify the setup, check these things:

1. Make sure babel-plugin-react-compiler and react-compiler-runtime are installed, as required for SDK 52.
2. Confirm that experiments.reactCompiler is set to true in your Expo app configuration.
3. Check that your Babel configuration uses the Expo preset and hasn't overridden the compiler configuration.
4. Restart Metro with a cleared cache using npx expo start --clear after changing Babel configuration.

You can also run npx react-compiler-healthcheck@latest to check whether your code follows the Rules of React, although this doesn't independently prove that compilation is happening.

My recommendation: Don't upgrade React Native solely to get the Memo ✨ indicator. First verify the compiler configuration. If you later upgrade to RN 0.78 or newer, you can use the DevTools indicator described in the release notes.

References:

• https://reactnative.dev/blog/2025/02/19/react-native-0.78
• https://docs.expo.dev/guides/react-compiler/