facebook/hermes
Hermes
Hermes is a mobile-optimized JavaScript runtime and engine designed for React Native. It functions as an ahead-of-time bytecode compiler that converts JavaScript source code into a dense binary format during the build process to eliminate the need for parsing and compilation at runtime.
The engine features a baseline JIT compiler that generates native machine code for frequently called functions to improve performance after the initial launch. It also includes a mobile-optimized garbage collector that precisely identifies reachable objects to minimize memory overhead and pause times on resource-constrained devices.
The project provides capabilities for ahead-of-time compilation, static analysis optimization, and compact bytecode representation to accelerate application startup and reduce memory usage. It also includes a command line tool to run JavaScript files and scripts.
Features
- JavaScript Engines - Functions as a high-performance JavaScript engine designed specifically to be integrated into React Native applications.
- React Native Performance Optimizations - Optimizes mobile app launch times and memory usage by providing a specialized JavaScript engine for React Native.
- Ahead-Of-Time Compilation - Compiles JavaScript source code into bytecode during the build process to eliminate runtime parsing overhead.
- Build-Time Bytecode Compilation - Provides a build-time process that compiles JavaScript source into bytecode to skip parsing and compilation at runtime.
- Bytecode Compilation - Transforms JavaScript source into a space-efficient bytecode format to reduce load times and memory usage.
- Cold Start Optimizations - Applies precompilation and static optimizations to drastically reduce the initial startup latency of mobile applications.
- Precise Garbage Collections - Implements a precise garbage collector that minimizes memory overhead and pause times on resource-constrained mobile devices.
- Mobile - Provides a JavaScript execution environment optimized for the resource constraints of mobile devices.
- Startup Optimizers - Minimizes application launch time by using static optimizations and compact bytecode to reduce initialization work.
- Mobile-Optimized Memory Management - Reduces pause times and memory overhead on mobile devices using a precise garbage collection system.
- JavaScript Engine Embedding - Designed to be embedded as the primary JavaScript execution engine within React Native host applications.
- Compact Binary Formats - Uses a dense executable format to reduce the total memory footprint and accelerate loading from disk.
- Compact Bytecode Representations - Employs a dense binary format for executable bytecode to reduce memory footprint and speed up loading.
- Static Analysis Optimizers - Performs static analysis during compilation to remove unused functions and execute constant folding.
- JIT Compilation Engines - Includes a baseline JIT compiler that generates native machine code for frequently called functions during execution.
- Event Loops - Utilizes a single-threaded event loop for processing asynchronous tasks and callbacks to ensure consistent state management.
- Garbage Collectors - Ships a precise garbage collector that minimizes memory overhead and pause times on resource-constrained mobile devices.
- Baseline JIT Compilation - Implements a baseline JIT compiler that generates native machine code for frequently called functions to improve runtime performance.
- Language Runtimes - JavaScript engine optimized for fast startup.
