Why Hermes engine in React Native? - Purpose & Use Cases

The Big Idea

What if your app could start instantly and run smoothly on any phone without extra coding?

The Scenario

Imagine building a React Native app that feels slow and clunky on older phones. You try to make it faster by tweaking JavaScript code, but the app still takes a long time to start and uses too much battery.

The Problem

Without a specialized engine, JavaScript runs slower because it must be interpreted every time. This causes delays in app startup and makes animations lag. It also drains battery faster, frustrating users and making your app look unprofessional.

The Solution

Hermes is a JavaScript engine optimized for React Native. It compiles JavaScript ahead of time, so the app starts faster and runs smoother. It reduces memory use and battery drain, giving users a better experience without extra work from you.

Before vs After

✗ Before

import React from 'react';
import { Text } from 'react-native';
// App runs with default JS engine, slower startup
export default function App() {
  return <Text>Hello</Text>;
}

✓ After

import React from 'react';
import { Text } from 'react-native';
// Enable Hermes engine in React Native config for faster startup
export default function App() {
  return <Text>Hello</Text>;
}

What It Enables

With Hermes, your React Native apps launch quickly and run smoothly even on low-end devices, delighting users everywhere.

Real Life Example

Think of a social media app that loads instantly when opened, with smooth scrolling and less battery drain—Hermes makes this possible by optimizing JavaScript execution behind the scenes.

Key Takeaways

Running JavaScript without optimization causes slow app startup and lag.

Hermes compiles JavaScript ahead of time for faster, smoother apps.

Using Hermes improves user experience on all devices, especially older ones.