Hermes on Windows + macOS
Hermes
The Hermes engine is an open source JavaScript engine created by Facebook to optimize building and running React Native applications.
To learn more about what it is and how to use it, check out the React Native documentation for it.
Hermes on Windows:
Hermes is experimentally supported on Windows, generally providing better performance characteristics than the default Chakra engine.
Enabling Hermes for new projects
Pass the --useHermes flag to react-native-windows-init when creating a new project. This will set up your project to use the Hermes engine and to generate bundles as Hermes bytecode instead of JavaScript.
Using Hermes in an existing project
Set the UseHermes property to true in the ExperimentalFeatures.props file in your project's windows directory:
<PropertyGroup Label="Microsoft.ReactNative Experimental Features">
...
<UseHermes>true</UseHermes>
</PropertyGroup>
Disabling Hermes
Set the UseHermes property to false in the ExperimentalFeatures.props file in your project's windows directory:
<PropertyGroup Label="Microsoft.ReactNative Experimental Features">
...
<UseHermes>false</UseHermes>
</PropertyGroup>
Known limitations
- CPU Sampling profiler is not yet supported
- Hermes is not yet compatible with other experimental features, like NuGet distribution or WinUI 3
- The binary for Hermes is not yet signed by Microsoft
- Debug builds of an app that uses Hermes are very slow
Hermes on macOS
Hermes is available on React Native for macOS, provided you are using version 0.62 or higher. To learn how to upgrade to the latest version, check out the Upgrading section of the macOS Getting Started guide.
After you have upgraded to the latest version of React Native for macOS, install and add the following:
- Install the npm package
yarn add 'hermes-engine-darwin@^0.4.3' - Add (or uncomment) the following pod dependencies to your macOS target in your
Podfile:
pod 'React-Core/Hermes', :path => '../node_modules/react-native-macos/'
pod 'hermes', :path => '../node_modules/hermes-engine-darwin'
pod 'libevent', :podspec => '../node_modules/react-native-macos/third-party-podspecs/libevent.podspec'
- Run
pod install
Be sure to set your target's deployment target to at least 10.14 before running
pod install