README.md

This is an example project to demonstrate the issue with esbuild and Hermes-compiled code. Due to certain esbuild optimizations, Hermes generates more bytecode compared to the standard Metro bundle.

It hepens for me with the folowing case: I use styled-components and react-native-gesture-handler and found that then more I have react-native-gesture-handler components wrapped into styled the more my hermes output bundle.

It seems the problem not in the styled-components and react-native-gesture-handler themself but more esbuild and hermes. The problem can be boiled down to the following code:

// TouchableOpacity.tsx
let Reanimated;

try {
    Reanimated = require('react-native-reanimated');
}  catch (e) {
    Reanimated = undefined;
}

export const TouchableOpacity = ({ children }) => {
    Reanimated.useSharedValue(0);
    return children;
};

// index.tsx
const { TouchableOpacity } from './TouchableOpacity'

const styled = (Component: React.ComponentType) => (styles: any) => {
    return (props: any) => <Component {...props} style={styles} />;
};

// input
const Comp = styled(View)``;

// output
// var _a;
// const Comp = styled(View)(_a || (_a = null));

It seems that the combination of _a || (_a = null) and (this part in the react-native-gesture-handler lib ) are contributing to the large bundle size.

How to reproduce

1. Run the script yarn copy-modules. This will generate 1000 copies of the ./src/template.tsx file.
2. Run ESBUILD=true yarn build to create the esbuild bundle.
3. Check the size of the ./output/index.android.bundle.hrs Hermes bundle.
4. Run ESBUILD=true yarn build to create the metro bundle.
5. Check the size of the ./output/index.android.bundle.hrs Hermes bundle.

Expected Result (ER): The size of the esbuild bundle should be less than or equal to the size of the Metro bundle.

Actual Result (AR): The size of the esbuild bundle (~2.7MB) is much larger than the bundle (~1.3MB) produced by Metro.