Hermes engine in React Native

Introduction

Hermes is a special tool that helps React Native apps run faster and use less battery. It makes your app feel smoother and quicker.

When you want your React Native app to start faster on Android devices.

When you want to reduce the app size to save space on users' phones.

When you want to improve battery life by making your app use less power.

When you want smoother animations and better overall app performance.

When you are building apps for users with older or slower phones.

Syntax

React Native

To enable Hermes in React Native, edit your android/app/build.gradle file:

project.ext.react = [
  enableHermes: true  // <- Set this to true to enable Hermes
]

Then rebuild your app.

Hermes is only available for Android and iOS (with some setup).

Enabling Hermes requires rebuilding your app to see the changes.

Examples

This turns Hermes on for your Android React Native app.

React Native

project.ext.react = [
  enableHermes: true
]

This turns Hermes off, using the default JavaScript engine.

React Native

project.ext.react = [
  enableHermes: false
]

Sample App

This simple React Native app shows a message confirming Hermes is enabled. You won't see Hermes directly, but enabling it makes this app start faster and run smoother.

React Native

import React from 'react';
import { Text, View } from 'react-native';

export default function App() {
  return (
    <View style={{flex:1, justifyContent:'center', alignItems:'center'}}>
      <Text>Hermes is enabled!</Text>
    </View>
  );
}

Important Notes

Hermes improves app start time and memory usage.

Debugging with Hermes is supported in modern React Native tools.

Always test your app after enabling Hermes to catch any issues.

Summary

Hermes is a JavaScript engine optimized for React Native apps.

It helps apps start faster and use less memory and battery.

Enable Hermes by setting enableHermes: true in your build config.