Hermes – JavaScript engine optimized for React Native

Hermes is a JavaScript engine optimized for fast start-up of React Native apps.

For many apps, enabling Hermes will result in improved start-up time, decreased memory usage, and smaller app size. At this time Hermes is an opt-in React Native feature,

This is free and open source software.

Key Features

• Ahead-of-time static optimization – build-time precompilation of JavaScript into efficient bytecode.
• Optimized for mobile – small in APK size, lean on memory, and starts instantly.
• Easy integration – implements JavaScript standards.
• Compact bytecode.
• Supports ECMAScript 2015 (ES6):
  • Symbols (including most well-known Symbols).
  • Iteration (with [Symbol.iterator]).
  • for..of loops.
  • Array spread.
  • Object rest/spread.
  • Shorthand property and computed property on object literals.
  • Destructuring assignment (with array and object “rest” properties).
  • Template string literals.
  • Generators (function* and yield).
  • TypedArrays.
  • Arrow functions.
  • Optional chaining and nullish coalescing (?. and ??).
  • Reflection (Reflect and Proxy).
  • Intl, or Internationalization APIs – currently Android only
  • ES6 Promise.
  • All ES6 JS library functions
    • Set/Map.
    • WeakSet/WeakMap.
    • ES6 String searching functions.
    • ES6 Array searching functions.

Website: hermesengine.dev
Support: GitHub Code Repository
Developer: Facebook, Inc. and its affiliates
License: MIT License

Hermes is written in C++. Learn C++ with our recommended free books and free tutorials.

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