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title React Native SDK (JSI) — Feature Flags for iOS & Android
description Integrate Checkgate's React Native SDK using JSI and C FFI for synchronous, bridge-free feature flag evaluation on iOS and Android. Compatible with Expo Dev Client.

React Native SDK (JSI)

The React Native SDK uses C FFI to call the Rust evaluation core directly from JavaScript via React Native's JavaScript Interface (JSI). This avoids the async bridge overhead and delivers synchronous, near-native evaluation performance.

Installation

npm install @checkgate/react-native
# or
yarn add @checkgate/react-native

iOS

cd ios && pod install

Android

The native library is linked automatically via CMake. No additional steps required.

Quick Start

import { CheckgateNativeClient } from '@checkgate/react-native'

const client = new CheckgateNativeClient({
  serverUrl: 'https://flags.yourcompany.com',
  sdkKey: 'your-sdk-key',
})

// Connect on app start (typically in App.tsx)
useEffect(() => {
  client.connect()
  return () => client.disconnect()
}, [])

// Evaluate flags synchronously anywhere
const enabled = client.isEnabled('new-onboarding', userId, {
  plan: user.plan,
  country: user.country,
})

API Reference

new CheckgateNativeClient(options)

Option Type Required Description
serverUrl string Yes Base URL of your Checkgate server
sdkKey string No SDK key for authentication
reconnectDelayMs number No SSE reconnect delay in ms (default: 5000)

client.connect(): void

Initiates the SSE connection in the background. Flags are loaded as they arrive; isEnabled() returns false for unknown flags during bootstrap.

Unlike the web SDK, connect() does not return a Promise — it fires and forgets, consistent with React Native's event-driven model.

client.isEnabled(flagKey, userKey, attributes): boolean

Synchronous flag evaluation via JSI. Runs on the JS thread, calls into the Rust library without bridging overhead.

client.disconnect(): void

Tears down the SSE connection. Call in your cleanup effect.

Usage with React Navigation

// App.tsx
import { NavigationContainer } from '@react-navigation/native'
import { CheckgateNativeClient } from '@checkgate/react-native'
import { createContext, useContext, useEffect, useState } from 'react'

const FlagContext = createContext<CheckgateNativeClient | null>(null)

export function useFlags() {
  return useContext(FlagContext)!
}

const flagClient = new CheckgateNativeClient({
  serverUrl: process.env.EXPO_PUBLIC_CHECKGATE_URL!,
  sdkKey: process.env.EXPO_PUBLIC_CHECKGATE_KEY,
})

export default function App() {
  useEffect(() => {
    flagClient.connect()
    return () => flagClient.disconnect()
  }, [])

  return (
    <FlagContext.Provider value={flagClient}>
      <NavigationContainer>
        {/* ... */}
      </NavigationContainer>
    </FlagContext.Provider>
  )
}
// screens/HomeScreen.tsx
import { useFlags } from '../App'
import { useUser } from '../hooks/useUser'

export function HomeScreen() {
  const flags = useFlags()
  const user = useUser()

  const showNewUI = flags.isEnabled('new-home-ui', user.id, {
    plan: user.plan,
    beta: user.isBeta ? 'true' : 'false',
  })

  return showNewUI ? <NewHomeUI /> : <LegacyHomeUI />
}

Expo Compatibility

The SDK is compatible with Expo managed workflow via the Expo Dev Client. It is not compatible with Expo Go (which doesn't support native modules).

npx expo install @checkgate/react-native
npx expo prebuild

Platform Support

Platform Architecture Status
iOS arm64 Supported
iOS Simulator x86_64 / arm64 Supported
Android arm64-v8a Supported
Android armeabi-v7a Supported
Android x86_64 Supported