React Native Shiki Engine

Oniguruma regex engine implementation for React Native, providing high-performance syntax highlighting capabilities through Shiki. This module implements a JSI-based native bridge to Oniguruma, enabling efficient pattern matching and syntax highlighting in React Native applications.

Important

React Native Shiki Engine requires the New Architecture to be enabled (react-native 0.71+)

Features

• High-performance native regex engine using Oniguruma, optimized for syntax highlighting
• Fully synchronous pattern matching with no async/await, no Promises, no Bridge
• Uses JSI and C++ TurboModules for direct JavaScript-to-native communication
• Smart pattern caching system for optimal performance
• Memory efficient with automatic cleanup of unused patterns
• Full compatibility with Shiki's regex engine requirements
• Written in modern C++ with robust memory management
• Multiple pattern support with efficient cache management

Installation

React Native

yarn add react-native-shiki-engine @shikijs/core
cd ios && pod install

You'll also need to install the languages and themes you want to use:

yarn add @shikijs/langs @shikijs/themes

Expo

npx expo install react-native-shiki-engine @shikijs/core @shikijs/langs @shikijs/themes
npx expo prebuild

For web support in Expo, also install:

npx expo install @shikijs/engine-oniguruma

Usage

Basic Integration

import { createHighlighterCore } from '@shikijs/core'
import javascript from '@shikijs/langs/javascript'
import nord from '@shikijs/themes/nord'
import { createNativeEngine, isNativeEngineAvailable } from 'react-native-shiki-engine'

if (!isNativeEngineAvailable()) {
  throw new Error('Native engine is not available')
}

const highlighter = await createHighlighterCore({
  themes: [nord],
  langs: [javascript],
  engine: createNativeEngine(),
})

const tokens = highlighter.codeToTokensBase(code, {
  lang: 'javascript',
  theme: 'nord',
})

Important

Performance Note: The Highlighter Instance

Create and maintain a single Highlighter instance at the app level. Avoid instantiating new highlighters inside components or frequently called functions.

Recommended:

• Store the highlighter instance in a global singleton or context
• Initialize it during app startup
• Reuse the same instance across your entire React Native application

Not Recommended:

• Creating new instances inside component render methods
• Initializing highlighters inside useEffect or event handlers
• Multiple instances for the same language/theme combination

See the examples directory for reference implementations using React Context to maintain a single highlighter instance.

Advanced Configuration

The native engine supports configuration options to optimize performance:

createNativeEngine({
  // Maximum number of patterns to cache
  maxCacheSize: 1000,
})

Web Platform Support (Expo)

For Expo apps targeting web, this native engine is not compatible as it relies on React Native's TurboModules and JSI. To support web platforms, use platform-specific files with Metro's .web.tsx extension.

Setup for Expo Web

1. Install the WASM engine:

npx expo install @shikijs/engine-oniguruma

2. Create platform-specific context files:

Native platforms (contexts/highlighter/index.tsx):

import { createHighlighterCore } from '@shikijs/core'
import javascript from '@shikijs/langs/javascript'
import nord from '@shikijs/themes/nord'
import { createNativeEngine } from 'react-native-shiki-engine'

const highlighter = await createHighlighterCore({
  themes: [nord],
  langs: [javascript],
  engine: createNativeEngine(),
})

Web platform (contexts/highlighter/index.web.tsx):

import { createHighlighterCore } from '@shikijs/core'
import { createOnigurumaEngine } from '@shikijs/engine-oniguruma'
import javascript from '@shikijs/langs/javascript'
import nord from '@shikijs/themes/nord'

const highlighter = await createHighlighterCore({
  themes: [nord],
  langs: [javascript],
  engine: createOnigurumaEngine(import('@shikijs/engine-oniguruma/wasm-inlined')),
})

Metro will automatically use the .web.tsx file when bundling for web, and the regular .tsx file for native platforms.

See the expo-app example for a complete implementation.

Technical Architecture

Native Implementation

The module uses a three-layer architecture optimizing for both performance and developer experience:

1. JavaScript Layer (src/)

   • TypeScript interfaces and JS wrapper for type safety
   • Efficient pattern lifecycle management with automatic cleanup
   • Seamless integration with Shiki's API
   • Error boundaries with graceful degradation

2. JSI Bridge (cpp/)

   • Zero-copy JavaScript-to-native communication
   • Smart pointer-based memory management
   • Thread-safe pattern caching with LRU eviction
   • Host object lifetime tracking

3. Oniguruma Core (vendored)

   • High-performance native regex engine
   • Optimized pattern matching with capture groups
   • Full Unicode support with UTF-8/16 encoding
   • Non-backtracking algorithm for predictable performance

Pattern Caching

The engine implements a sophisticated multi-level caching system:

• L1 Cache: Hot patterns in JSI host objects

  • Zero-copy access from JavaScript
  • Reference-counted lifetime management
  • Automatic cleanup on context destruction

• L2 Cache: Compiled patterns in native memory

  • LRU eviction with generational collection
  • Adaptive sizing based on memory pressure
  • Thread-safe concurrent access
  • Configurable eviction policies

• Memory Management

  • Proactive cleanup of unused patterns
  • Automatic defragmentation
  • Memory pressure handling
  • Configurable high/low watermarks

Supported Platforms

Platform	Architecture	Description	Status
iOS Simulator	x86_64	Intel-based simulators	✅
iOS Simulator	arm64	Apple Silicon simulators	✅
iOS Device	arm64	All modern iOS devices	✅
Android	arm64-v8a	Modern Android devices (64-bit ARM)	✅
Android	armeabi-v7a	Older Android devices (32-bit ARM)	✅
Android	x86	Android emulators (32-bit Intel/AMD)	✅
Android	x86_64	Android emulators (64-bit Intel/AMD)	✅

Contributing

Contributions are welcome! Please read our Contributing Guide for details on:

• Code of conduct
• Development workflow
• Pull request process
• Coding standards

License

MIT License - see the LICENSE file for details

Acknowledgments

• Shiki - The beautiful yet powerful syntax highlighter we bring to React Native
• Oniguruma - The blazing-fast regex engine powering our native implementation
• React Native - Making native module development possible with JSI and TurboModules

Support

For questions, bug reports, or feature requests:

• GitHub Issues
• GitHub Discussions