Improve React Native Android Startup Time by Disabling `.bundle` Compression

#reactnative #android #mobile

There's a simple optimization that can significantly reduce startup time—disabling compression for .bundle files.

🎯 The Optimization

Margelo, a well-known tech company in the React Native ecosystem, recently shared a pro tip:

🚀 Disabling compression for .bundle files can improve launch speed by up to 400ms.

You can apply this optimization by modifying your app/build.gradle file:

android {
    androidResources {
        noCompress += ["bundle"]
    }
}

🔍 How It Works

By default, Android compresses .bundle files, requiring them to be decompressed during runtime. This adds overhead to the app's launch process.

By adding .bundle files to noCompress, we allow Android to load them directly, reducing startup delay.

🏎️ Result: Faster app launch time 🚀

✅ Compatibility

A common concern among developers is:

"Does this optimization work for both the old and new React Native architectures?"

Answer: Yes!

React Native core contributor Marc (mrousavy) confirmed that this works for both architectures, making it a safe and effective improvement for all projects.

⚖️ Trade-Offs: Faster Startup vs. APK Size

While this tweak improves startup performance, there's a small trade-off:

🔴 Slightly Increased APK Size

Since .bundle files are no longer compressed, they take up more disk space in the APK.

However, in most cases, faster launch times outweigh the minimal size increase, leading to a better user experience.

📉 How to Manage APK Size?

If your app size increases significantly, here are some tips:

✅ Reduce unused dependencies in your .bundle file.

✅ Use Proguard and R8 to remove unused code.

✅ Optimize images and assets for better compression.

✅ Enable Hermes for better performance and reduced bundle size.