Hermes is an open-source JavaScript engine developed by Facebook, specifically designed to improve the startup time of React Native apps. It was first introduced in React Native 0.60.4 in 2019.
React Native apps are typically written in JavaScript, and this code is interpreted by a JavaScript engine before being executed on a device. Previously, most React Native apps used JSC (JavaScriptCore) for code interpretation. However, with an aim to enhance performance, especially for mobile apps, Facebook introduced Hermes.
The key features and advantages of Hermes are:
- Fast Startup Time: As Hermes directly executes JavaScript compiled into bytecode, it enhances the app's startup time.
- Low Memory Footprint: Hermes is designed to minimize memory usage, thereby reducing the overall memory consumption of the app.
- Optimized for React Native: Hermes is optimized for use with React Native, offering potential performance improvements for typical React Native operations.
For more information, check out the blog What is Hermes Engine?.