Ship compressed JS bundles

Warning: not yet available for Android.

Sometimes you need a very small .app, for example if you are building an App Clip. (App Clips have to be strictly less than 10 MB in their _ uncompressed_ form.)

When you distribute your React Native app, JavaScript code gets bundled into a .jsbundle file. It can get quite large.

This package allows you to compress your .jsbundle when you build the app for distribution. When the app is run, it automatically uncompresses the .jsbundle on the fly.

How does it work?

react-native-compressed-jsbundle provides:

  • A script that automatically compresses your .jsbundle using the fast and compact Brotli algorithm;
  • a custom .jsbundle loader that uncompresses the .jsbundle (at ~350MB/s) at app launch. The loader uses standard mechanisms for loading customization that React Native provides.



Add the library a dependency:

$ yarn add react-native-compressed-jsbundle

Open your Xcode project and modify the React Native build phase (“Bundle React Native code and images”):

export NODE_BINARY=node

# 1. Add this line at the bottom of the script.

Open AppDelegate.m and add the following:

// 2. Add the new import directive below other imports.
#import <react-native-compressed-jsbundle/IMOCompressedBundleLoader.h>

@implementation AppDelegate

// Other methods

// 3. Add the following lines below other methods:
- (void)loadSourceForBridge:(RCTBridge *)bridge onProgress:(RCTSourceLoadProgressBlock)onProgress onComplete:(RCTSourceLoadBlock)loadCallback {
  [IMOCompressedBundleLoader loadSourceForBridge:bridge bridgeDelegate:self onProgress:onProgress onComplete:loadCallback];


You are good to go.


This libary does add a bit of time to app startup due to the decompression step. However, it is quite small – around 20ms for a 5 MB .jsbundle.

I have included some simple low-overhead tracing in the library, so you can see for yourself whether the tradeoff is acceptable. Build your app in Release mode on your device and look into the Xcode console.