feat(react-native): add $react_native_version to captured events

.changeset/core-flag-called-react-native-version.md

@@ -0,0 +1,5 @@
+---
+'@posthog/core': patch
+---
+
+Keep `$react_native_version` on minimal `$feature_flag_called` events

.changeset/react-native-version-property.md

@@ -0,0 +1,5 @@
+---
+'posthog-react-native': minor
+---
+
+Add `$react_native_version` (for example `0.79.6`) to events captured from JavaScript

packages/core/src/featureFlagUtils.ts

@@ -252,6 +252,8 @@ export const MINIMAL_FLAG_CALLED_EVENT_PROPERTIES: readonly string[] = [
   '$lib_version',
   '$device_id',
   '$is_server',
+  // Runtime identity, kept for runtime breakdowns of flag calls
+  '$react_native_version',
 ]
 
 /**

packages/react-native/references/posthog-react-native-references-latest.json

@@ -3347,6 +3347,11 @@
           "type": "string | null",
           "name": "$os_version"
         },
+        {
+          "description": "React Native version like \"0.79.6\"",
+          "type": "string | null",
+          "name": "$react_native_version"
+        },
         {
           "description": "Timezone of the device like \"Europe/Berlin\"",
           "type": "string | null",

packages/react-native/src/native-deps.tsx

@@ -1,5 +1,5 @@
 import { OptionalAsyncStorage } from './optional/OptionalAsyncStorage'
-import { GLOBAL_OBJ, getPlatformOS, isMacOS, isWeb, isWindows } from './utils'
+import { GLOBAL_OBJ, getPlatformOS, getReactNativeVersion, isMacOS, isWeb, isWindows } from './utils'
 import { OptionalExpoApplication } from './optional/OptionalExpoApplication'
 import { OptionalExpoDevice } from './optional/OptionalExpoDevice'
 import { OptionalExpoFileSystem } from './optional/OptionalExpoFileSystem'
@@ -39,6 +39,11 @@ export const getAppProperties = (): PostHogCustomAppProperties => {
     $device_type: currentDeviceType,
   }
 
+  const reactNativeVersion = getReactNativeVersion()
+  if (reactNativeVersion) {
+    properties.$react_native_version = reactNativeVersion
+  }
+
   if (OptionalExpoApplication) {
     properties.$app_build = OptionalExpoApplication.nativeBuildVersion
     properties.$app_name = OptionalExpoApplication.applicationName

packages/react-native/src/types.ts

@@ -154,6 +154,8 @@ export interface PostHogCustomAppProperties {
   $timezone?: string | null
   /** Whether the app is running on an emulator/simulator */
   $is_emulator?: boolean | null
+  /** React Native version like "0.79.6" */
+  $react_native_version?: string | null
 }
 
 export type PostHogSessionReplayConfig = {

packages/react-native/src/utils.ts

@@ -51,3 +51,20 @@ export function isWindows(): boolean {
 }
 
 export const isHermes = () => !!GLOBAL_OBJ.HermesInternal
+
+type ReactNativeVersion = { major: number; minor: number; patch: number; prerelease?: number | string | null }
+
+/** React Native version like "0.79.6" or "0.80.0-rc.2", or undefined where Platform.constants doesn't report it (e.g. web) */
+export function getReactNativeVersion(): string | undefined {
+  try {
+    const version = (Platform as { constants?: { reactNativeVersion?: ReactNativeVersion } }).constants
+      ?.reactNativeVersion
+    if (!version || typeof version.major !== 'number') {
+      return undefined
+    }
+    const { major, minor, patch, prerelease } = version
+    return `${major}.${minor}.${patch}${prerelease != null ? `-${prerelease}` : ''}`
+  } catch {
+    return undefined
+  }
+}

packages/react-native/test/react-native-version.spec.ts

@@ -0,0 +1,67 @@
+import { Platform } from 'react-native'
+import { minimizeFlagCalledEventProperties } from '@posthog/core'
+import { PostHog } from '../src'
+import { getReactNativeVersion } from '../src/utils'
+
+const platform = Platform as typeof Platform & { constants?: unknown }
+
+describe('$react_native_version', () => {
+  afterEach(() => {
+    delete platform.constants
+  })
+
+  it('formats Platform.constants.reactNativeVersion', () => {
+    platform.constants = { reactNativeVersion: { major: 0, minor: 79, patch: 6, prerelease: null } }
+    expect(getReactNativeVersion()).toBe('0.79.6')
+  })
+
+  it('appends the prerelease tag', () => {
+    platform.constants = { reactNativeVersion: { major: 0, minor: 80, patch: 0, prerelease: 'rc.2' } }
+    expect(getReactNativeVersion()).toBe('0.80.0-rc.2')
+  })
+
+  it('is undefined when the platform does not report a version', () => {
+    platform.constants = {}
+    expect(getReactNativeVersion()).toBeUndefined()
+  })
+
+  it('is undefined when the version object has no numeric fields', () => {
+    platform.constants = { reactNativeVersion: {} }
+    expect(getReactNativeVersion()).toBeUndefined()
+  })
+
+  it('is undefined when reading the constants throws', () => {
+    Object.defineProperty(platform, 'constants', {
+      configurable: true,
+      get: () => {
+        throw new Error('getConstants failed')
+      },
+    })
+    expect(getReactNativeVersion()).toBeUndefined()
+  })
+
+  it('is sent with every event', async () => {
+    platform.constants = { reactNativeVersion: { major: 0, minor: 79, patch: 6 } }
+    const posthog = new PostHog('test-token', { flushInterval: 0 })
+    await posthog.ready()
+
+    expect(posthog.getCommonEventProperties().$react_native_version).toBe('0.79.6')
+
+    await posthog.shutdown()
+  })
+
+  it('survives minimal $feature_flag_called events', () => {
+    expect(minimizeFlagCalledEventProperties({ $react_native_version: '0.79.6', custom: 'dropped' })).toEqual({
+      $react_native_version: '0.79.6',
+    })
+  })
+
+  it('is omitted when the platform does not report a version', async () => {
+    const posthog = new PostHog('test-token', { flushInterval: 0 })
+    await posthog.ready()
+
+    expect(posthog.getCommonEventProperties()).not.toHaveProperty('$react_native_version')
+
+    await posthog.shutdown()
+  })
+})