Hermes V1

Hermesv1 is currently only an experimental feature and is not enabled by default; at present, it can only be guaranteed to function normally.

Step 1: Build Hermes V1 binaries(**Only macOS can build)

pnpm build:hermesv1

Step 2: Configure Hermes compiler override

Add the Hermes V1 compiler package override to your root package.json.

"pnpm": {
  "overrides": {
    "hermes-compiler": "250829098.0.9"
  }
}

Then install the overridden package:

pnpm install

Step 3: Bundle JavaScript with Hermes V1 compiler

cd packages/tester
pnpm bundle:hermesv1

Step 4: Configure native build for V1 runtime

Option A: Edit CMakeLists.txt

Edit packages/tester/harmony/react_native_openharmony/src/main/cpp/RNOH/JSEngine/hermes/CMakeLists.txt:

# Change line 1 from:
set(HERMES_V1_ENABLED OFF CACHE BOOL "Build with support for Hermes v1")

# To:
set(HERMES_V1_ENABLED ON CACHE BOOL "Build with support for Hermes v1")

Option B: Pass CMake argument

Add to your cmake build configuration (exact method depends on your setup):

-DHERMES_V1_ENABLED=ON

Step 5: Build and run the app

Verification

1. Build logs: Look for HERMES_V1_ENABLED is set to: ON in CMake output
2. Bytecode version: Run the following command and validate if #0x62 is printed

objdump -d packages/tester/harmony/react_native_openharmony/src/main/cpp/third-party/prebuilt/debug/arm64-v8a/libhermesvm.so | grep -A 2 getBytecodeVersion | grep "mov.*#0x" | awk '{print $5, $6}'

Note: Requires objdump/binutils. If unavailable, skip to runtime verification. 3. Runtime: Calling the following method should return "250829098.0.9" in Hermes V1

HermesInternal.getRuntimeProperties()['OSS Release Version'];