Hermes

Readme.md

Hermes

• Hermes JS Engine

  • In Hermes Ahead-Of-Time (AOT) compilation means the translation of JavaScript code to Herems byte code.
  • Hermes has both, a single-threaded, generational, stop the world GC called GenGC and a concurrent GC called Hades which seems to be the default GC. Concurrent GC seems to be only implemented on 64-bit architectures (see Incremental Mode).
  • Internally uses AsmJit to generate code. AsmJit currently supports 32-bit and 64-bit X86, AArch64, and AArch32 in a separate testing branch. The Hermes JIT itself currently only supports AArch64.
  • JSI (JavaScript Interface) is Hermes' JS to Native interface that enables direct communication between native code and JavaScript (also see Tzvetan's Hermes JSI Demos).
    • There's an ongoing discussion in Hermes about support for the Node-API instead or in addition to JSI (see Using Rust in react-native with jsi-rs for a comparison of the different approaches).

• How to try Static Hermes (Discussion in the hermes repository)

• Static Hermes for React Native (PR in the react-native repository)

• Static Hermes and JIT? (Reddit thread)

• Static Hermes with Tzvetan Mikov (React Native Radio, Episode 323, Feb 2025)

  • Talks about JIT compilation of JS to native code?
  • Static Hermes will replace Hermes for untyped JS in 2025.

• Neil Dhar: Optimizing with Static Hermes (Chain React, 2024)

  • Sound Types (i.e. proving correctness of Typescript/Flow type annotations)
  • Inlining
  • Object Elision (aka Scalar Replacement)

• Tzvetan Mikov's tweet on Static Hermes running Octane (GitHub repo)

  • Compares WebKit's JavaScriptCore (jsc), Google's V8 and QuickJS Javascript Engine with Hermes and Static Hermes.

• Tzvetan Mikov: Hermes: better performance with runtime bytecode translation (React Universe Conf, 2024) (slisdes)

  • Bytecode translation (to native) on the device (seems to be a very simple JIT similar to an "unrolled" Template Interpreter).
  • Static Hermes has two back ends: one produces bytecode and the other one native code with the help of LLVM.

• Tzvetan Mikov: Static Hermes: How to Speed Up a Micro-benchmark by 300x Without Cheating (Blog post, Sep 2023)

• Tzvetan Mikov: Static Hermes: the Next Generation of Hermes (React Native EU, 2023) (slides)

  • Introducing Static Hermes
  • AOT compilation of JS to native based on "sound typing" (Typescript/Flow)
  • Zero cost foreign function interface (aka native calls) based on JSI.

• Tzvetan Mikov: Improving React Native Performance (React Native EU, 2019)

  • Introducing Hermes
  • Hermes AOT: JS -> AST -> SSA -> Optimizations (inlining, common subexpression elimination, constant folding/propagation, type inference) -> Bytecode (variable length, register machine)

• Flow - a static type checker for JavaScript

  • GitHub repository

ReactNative

• Exploring the Depths of React Native’s New Architecture: Hermes, JSI, Fabric, Yoga, Turbo Module, and Codegen (Blog post, 2023)

• React Native for Windows + macOS - Microsoft's fork of ReactNative with support for Windows SDK as well as the macOS 10.14 SDK.

  • Builds native Windows apps for all devices supported by Windows 10 and higher including PCs, tablets, 2-in-1s, Xbox, Mixed reality devices, etc., as well as the macOS desktop and laptop ecosystems.
  • GitHub repository
  • Uses Microsoft's own fork of Hermes