In the world of mobile app development, React Native has emerged as a popular choice for building cross-platform applications efficiently. With its ability to write code in JavaScript and render native components, React Native has gained widespread adoption among developers. One of the key features that has been introduced in React Native version 0.60 is Hermes, a JavaScript engine designed to improve app performance. However, with the introduction of Hermes in React Native version 0.71, compatibility issues have arisen with tools like React Native Debugger. This has led developers to seek ways to disable Hermes during development and enable it automatically in production.
In this article, we will explore the various methods and best practices for using Hermes in React Native development, how to enable/disable Hermes based on the platform (Android/iOS), configuring JavaScript engines, and adding commands to enable and disable Hermes in Expo. We will also discuss the challenges and crashes that may occur while enabling Hermes in Expo development builds.
Using Hermes
Hermes is a JavaScript engine developed by Facebook that focuses on improving app performance by reducing memory usage and improving startup time. Enabling Hermes in React Native can lead to significant performance improvements, especially on low-end devices. When Hermes is enabled, the JavaScript code is ahead-of-time (AOT) compiled during the build process, resulting in faster app startup times.
To enable Hermes in a React Native project, you can add the following configuration to your `app/build.gradle` file:
```gradle
project.ext.react = [
enableHermes: true
This will tell React Native to use Hermes as the JavaScript engine for your Android app. For iOS, you can enable Hermes by adding the following configuration to your `Podfile`:
```ruby
use_react_native!(:path => config[:reactNativePath], # change path to dependency on React Native
hermes_enabled: true)
Using Hermes Engine
Hermes Engine is a standalone JavaScript engine that can be used in place of the default JavaScriptCore engine in React Native. By using Hermes Engine, you can take advantage of Hermes' performance improvements without having to enable Hermes in the React Native project.
To use Hermes Engine in your React Native project, you can follow these steps:
1. Install the Hermes Engine package using npm or yarn:
```bash
npm install @hermes-engine/react-native-bridge
2. Link the Hermes Engine package to your React Native project:
```bash
npx react-native link @hermes-engine/react-native-bridge
3. Configure the Hermes Engine in your project settings to use it as the default JavaScript engine.
By using Hermes Engine, you can leverage Hermes' performance benefits without the need to enable Hermes in your React Native project.
How to Enable/Disable Hermes Based on Android/iOS
Enabling and disabling Hermes based on the platform (Android/iOS) can be achieved by modifying the project configuration files for each platform. As mentioned earlier, you can enable Hermes in Android by adding the `enableHermes: true` configuration in the `app/build.gradle` file. For iOS, you can enable Hermes by setting `hermes_enabled: true` in the `Podfile`.
To disable Hermes for development purposes, you can create separate build configurations for development and production environments. For example, you can have a `debug` configuration for development builds that disables Hermes and a `release` configuration for production builds that enables Hermes. By switching between these configurations, you can control whether Hermes is enabled or disabled based on the build type.
Configure JS Engines
In addition to Hermes, React Native supports other JavaScript engines like JavaScriptCore and V8. By configuring the JavaScript engine in your React Native project, you can customize the runtime behavior and performance characteristics of your app.
To configure the JavaScript engine in your React Native project, you can specify the engine type in the project settings. For example, you can set `jsEngine: 'hermes'` to use Hermes as the JavaScript engine, or `jsEngine: 'jsc'` to use JavaScriptCore.
By configuring the JavaScript engine, you can optimize the performance of your React Native app and tailor it to your specific requirements.
Add Command to Enable & Disable Hermes for Expo #2217
In Expo projects, enabling and disabling Hermes can be achieved by adding custom commands to the project configuration. Issue #2217 on the Expo GitHub repository discusses the implementation of commands to enable and disable Hermes in Expo projects.
To add a command to enable Hermes in Expo, you can modify the project configuration to set the `enableHermes` flag to true. Similarly, to disable Hermes, you can set the `enableHermes` flag to false.
By adding custom commands to enable and disable Hermes in Expo, you can streamline the development process and optimize the performance of your Expo projects.
current url：https://dwzrug.e538c.com/bag/expo-disable-hermes-71618