Base Bytecode Optimization

Base bytecode optimization generates your new Hermes bundle using the previously shipped bundle (the "base") as a reference. This was acheived by passing a flag --base-bytecode <path-to-base-bundle> to the Hermes CLI while generating the new bundle. This results in a smaller patch bundle because only the bytecode differences are transmitted (vs. the base).

Size Comparison

File Size Comparison

Bundle Type	Original	With Deflate	With Brotli
Uncompressed Full Bundle	24.5 MB	11.04 MB	8.14 MB
Uncompressed Patch Bundle	~24.5 MB	3.82 MB	2.9 MB
Uncompressed Patch Bundle With Base Bytecode	~24.5 MB	1.1 MB	0.8 MB (96% smaller🔥)

Compatibility

Available starting from SDK v1.2.0.

Enable Base Bytecode Optimization

To use this feature, set the path to the old bundle saved in the Patch Update Guide - Step 1. You’ll use this as the base when generating the new bundle in Step 3 of the Patch Update Guide.

Android

Either set the environment variable or use the gradle.properties file.

# Environment variable
export DOTA_BASE_BUNDLE_PATH=.dota-versions/v1.0.0-android/index.android.bundle && ./gradlew assembleRelease

# gradle.properties
dotaBaseBundlePath=.dota-versions/v1.0.0-android/index.android.bundle

iOS

React Native does not directly expose --base-bytecode flag for iOS, so we add support via a patch to react-native-xcode.sh using patch-package.

1. Install patch-package (skip if already installed):

yarn add patch-package postinstall-postinstall --dev

Add to package.json:

{
  "scripts": {
    "postinstall": "patch-package"
  }
}

2. Modify node_modules/react-native/scripts/react-native-xcode.sh to pass the base bytecode flag to Hermes. Insert before the Hermes CLI execution block:

# Inside react-native-xcode.sh

BASE_BYTECODE_PATH=""
if [[ ! -z $DOTA_BASE_BUNDLE_PATH ]]; then
  if [[ -f $DOTA_BASE_BUNDLE_PATH ]]; then
    BASE_BYTECODE_PATH="--base-bytecode $DOTA_BASE_BUNDLE_PATH"
    echo "Using --base-bytecode with path: $DOTA_BASE_BUNDLE_PATH"
  else
    echo "Not using --base-bytecode, path: $DOTA_BASE_BUNDLE_PATH, file not found"
    BASE_BYTECODE_PATH=""
  fi
fi

"$HERMES_CLI_PATH" -emit-binary -max-diagnostic-width=80 $EXTRA_COMPILER_ARGS -out "$DEST/$BUNDLE_NAME.jsbundle" "$BUNDLE_FILE" $BASE_BYTECODE_PATH

Create the patch:

yarn patch-package react-native

3. Provide the base bundle path via env var (use the old bundle path saved in .dota-versions/):

# .xcode.env
export DOTA_BASE_BUNDLE_PATH=.dota-versions/v1.0.0-ios/main.jsbundle

# Inline when building
export DOTA_BASE_BUNDLE_PATH=.dota-versions/v1.0.0-ios/main.jsbundle && yarn ios --mode=Release

info

Follow every step in the Patch Update Guide; this feature only adds one extra action just before generating the new bundle (set the base bundle path).

Note

If you are using manual bundle generation as described in Bundle Generation Guide, pass --base-bundle-path <path-to-old-bundle> to the CLI.

Disable Base Bytecode Optimization

To disable this feature, unset the DOTA_BASE_BUNDLE_PATH environment variable.

Verify Base Bytecode Optimization

To verify that the base bytecode optimization is enabled, you can check the size of the patch bundle being downloaded. Use sync API to verify the size of the patch bundle being downloaded.

codePush.sync(
  {},
  (status) => {
    console.log(status);
  },
  ({ receivedBytes, totalBytes }) => {
    console.log(`Downloaded ${receivedBytes} of ${totalBytes} bytes`);
  }
);

Base bytecode optimization enabled

✅ Setup complete. Your next bundle builds will use the saved base to produce smaller patch bundles. Continue with create‑patch and release steps in the Patch Update Guide.