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What is this?

React Native gives your product one main JavaScript runtime. When a feed, chat screen, editor, reducer, or hydration job monopolizes that runtime, input, animation, and navigation all start competing for the same VM.

react-native-runtimes adds a multi-runtime layer for React Native New Architecture apps:

• mount selected React components in named secondary Hermes runtimes
• run whole screens, headless tasks, and typed functions away from the main runtime
• share state across isolated JS heaps through a native C++ singleton
• prewarm runtimes before navigation so expensive surfaces are ready when users arrive
• wire it through Metro and, for Expo, a config plugin instead of hand-written runtime plumbing

// That's it. This component now renders in its own Hermes instance.
<OnRuntime name="chat-runtime">
  <MessageList conversationId={conversationId} />
</OnRuntime>

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What it unlocks

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When to reach for it

• You have one or two expensive features that repeatedly monopolize the main JS runtime.
• You want a chat, feed, editor, map sidebar, or media-heavy route to stay alive and warm.
• You need business logic or cache hydration to run without blocking interaction.
• You are already on React Native New Architecture with Hermes, or you are willing to move there.

When not to use it

• Your app is simple enough that memoization, virtualization, or moving work off render fixes the issue.
• You need legacy architecture or a non-Hermes JS engine.
• You want to pass large mutable objects or non-serializable props directly between runtimes. Pass ids/keys and read shared data from native-backed state instead.

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Packages

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Core capabilities

🧵 Zero-boilerplate threaded components

Wrap a component in OnRuntime — Metro rewrites the JSX to a registered threaded boundary at build time. No manual registration required.

import { OnRuntime } from '@react-native-runtimes/core';

<OnRuntime name="feed-runtime">
  <HeavyFeedList userId={userId} />
</OnRuntime>

📱 Full-screen threaded routes

For navigation flows that should live entirely on a secondary runtime:

import { ThreadedScreen, threadedComponent } from '@react-native-runtimes/core';

export const ConversationScreen = threadedComponent<Props>(
  'ConversationScreen',
  (props) => <ConversationRoute {...props} />,
);

// In your navigator:
<ThreadedScreen
  component={ConversationScreen}
  props={{ conversationId }}
  runtimeName={`chat-${conversationId}`}
/>

⚡ Runtime prewarming

Start the runtime before the user navigates so there is no cold-start lag:

import { ThreadedRuntime } from '@react-native-runtimes/core';

// e.g. when the inbox row becomes visible
await ThreadedRuntime.prewarm(`chat-${conversationId}`);

🏃 Headless tasks

Run JS on a named runtime without mounting a view — perfect for pre-hydrating stores, decoding data, or running reducers in a long-lived worker:

// Register on the threaded bundle side:
registerThreadedHeadlessTask('hydrateConversation', async ({ payload }) => {
  const messages = await loadMessages(payload.conversationId, payload.limit);
  await messagesStore.setSubtreeState(payload.conversationId, messages, true);
});

// Dispatch from anywhere:
await ThreadedRuntime.runHeadlessTask('hydrateConversation', {
  runtimeName: 'chat-worker-runtime',
  payload: { conversationId, limit: 50 },
});

🔀 Cross-runtime function calls

Call a typed function on a specific runtime and await the result — arguments and return values are JSON-serialized automatically:

import { call, runtimeFunction } from '@react-native-runtimes/core';

export const fibonacci = runtimeFunction((n: number) => ({
  input: n,
  result: fibonacciNumber(n),
  computedAt: new Date().toISOString(),
}));

// Call it on a named runtime from the main runtime:
const result = await call(fibonacci).on('fibonacci-worker-runtime')(38);

Or use a function directive for fixed-runtime helpers — Metro rewrites the call site automatically:

async function refreshCache(key: string) {
  'background'; // ← directive: this function always runs on 'background' runtime
  await cacheStore.hydrate();
  return cacheStore.get(key);
}

const value = await refreshCache('settings'); // cross-runtime, no extra API

🗂 Shared state — synchronous, cross-heap

A Zustand-style API backed by a native C++ process-wide singleton. Reads are synchronous. No bridge round-trip. Any runtime can write and every subscriber is notified.

import { createSharedStore } from '@react-native-runtimes/state';

export const chatStore = createSharedStore({
  name: 'chat',
  initialState: { messages: {}, settings: { theme: 'dark' } },
});

// Path handles for fine-grained subscriptions:
const roomMessages = chatStore.path<Message[]>(['messages', 'release-room']);

await roomMessages.update(items => [...(items ?? []), newMessage]);

// Subscribe with a selector — works in any runtime:
const count = roomMessages.use(items => items?.length ?? 0);

Add native persistence with a single option:

export const preferencesStore = createSharedStore({
  name: 'preferences',
  initialState: { counter: { count: 0 } },
  persist: { key: 'preferences', version: 1, subtrees: ['counter'] },
});

🏗 Business runtimes

For an app-lifetime runtime that sees the same native modules as the main runtime, use prewarmBusinessRuntime:

ThreadedRuntime.setMainReactPackagesProvider { PackageList(this).packages }
ThreadedRuntime.prewarmBusinessRuntime(applicationContext, "business-runtime")

if (global.__THREADED_RUNTIME_ENV__?.kind === 'business-runtime') {
  require('./src/businessRuntimeEntry');
}

🔌 Expo support

@react-native-runtimes/core ships a config plugin. No manual native edits needed:

// app.config.ts
export default {
  newArchEnabled: true,
  plugins: [
    ['@react-native-runtimes/core', {
      packages: ['@react-native-runtimes/state'],
    }],
  ],
};

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Getting Started

1. Install

npm install @react-native-runtimes/core @react-native-runtimes/state react-native-nitro-modules

2. Configure Metro

// metro.config.js
const { getDefaultConfig, mergeConfig } = require('@react-native/metro-config');
const { withThreadedRuntime } = require('@react-native-runtimes/core/metro');

module.exports = withThreadedRuntime(
  mergeConfig(getDefaultConfig(__dirname), {}),
  { roots: ['App.tsx', 'src'], generatedDir: '.threaded-runtime' },
);

3. Load the generated entry

// index.js
if (global.__THREADED_RUNTIME_ENV__) {
  require('./.threaded-runtime/entry');
} else {
  require('./App');
}

4. Render

import { OnRuntime } from '@react-native-runtimes/core';

export default function App() {
  return (
    <OnRuntime name="my-runtime">
      <HeavyComponent />
    </OnRuntime>
  );
}

→ Full setup guide: packages/core/README.md

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Requirements

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Documentation

• 📖 Hosted docs
• 📦 Core package — full API reference
• 🗂 State package — shared store API
• 🧪 Example app
• 🏗 Docusaurus source
• 🤝 Contributing guide

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Authors

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