feat: Save the $screen_name on every event (#100)

posthog-core/src/index.ts

@@ -584,6 +584,7 @@ export abstract class PostHogCore extends PostHogCoreStateless {
   // internal
   protected _decideResponsePromise?: Promise<PostHogDecideResponse | undefined> // TODO: come back to this, fix typing
   protected _sessionExpirationTimeSeconds: number
+  protected sessionProps: PostHogEventProperties = {}
 
   constructor(apiKey: string, options?: PosthogCoreOptions) {
     // Default for stateful mode is to not disable geoip. Only override if explicitly set
@@ -632,6 +633,7 @@ export abstract class PostHogCore extends PostHogCoreStateless {
 
   private clearProps(): void {
     this.props = undefined
+    this.sessionProps = {}
   }
 
   private _props: PostHogEventProperties | undefined
@@ -669,9 +671,10 @@ export abstract class PostHogCore extends PostHogCoreStateless {
     }
   }
 
-  private enrichProperties(properties?: PostHogEventProperties): any {
+  public enrichProperties(properties?: PostHogEventProperties): any {
     return {
       ...this.props, // Persisted properties first
+      ...this.sessionProps, // Followed by session properties
       ...(properties || {}), // Followed by user specified properties
       ...this.getCommonEventProperties(), // Followed by FF props
       $session_id: this.getSessionId(),
@@ -707,6 +710,11 @@ export abstract class PostHogCore extends PostHogCoreStateless {
     return this.getPersistedProperty<string>(PostHogPersistedProperty.DistinctId) || this.getAnonymousId()
   }
 
+  unregister(property: string): void {
+    delete this.props[property]
+    this.setPersistedProperty<PostHogEventProperties>(PostHogPersistedProperty.Props, this.props)
+  }
+
   register(properties: { [key: string]: any }): void {
     this.props = {
       ...this.props,
@@ -715,9 +723,15 @@ export abstract class PostHogCore extends PostHogCoreStateless {
     this.setPersistedProperty<PostHogEventProperties>(PostHogPersistedProperty.Props, this.props)
   }
 
-  unregister(property: string): void {
-    delete this.props[property]
-    this.setPersistedProperty<PostHogEventProperties>(PostHogPersistedProperty.Props, this.props)
+  registerForSession(properties: { [key: string]: any }): void {
+    this.sessionProps = {
+      ...this.sessionProps,
+      ...properties,
+    }
+  }
+
+  unregisterForSession(property: string): void {
+    delete this.sessionProps[property]
   }
 
   /***

posthog-core/test/posthog.register.spec.ts

@@ -0,0 +1,42 @@
+import { PostHogPersistedProperty } from '../src'
+import { createTestClient, PostHogCoreTestClient, PostHogCoreTestClientMocks } from './test-utils/PostHogCoreTestClient'
+
+describe('PostHog Core', () => {
+  let posthog: PostHogCoreTestClient
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  let mocks: PostHogCoreTestClientMocks
+
+  beforeEach(() => {
+    ;[posthog, mocks] = createTestClient('TEST_API_KEY', {})
+  })
+
+  describe('register', () => {
+    it('should register properties to storage', () => {
+      posthog.register({ foo: 'bar' })
+      expect(posthog.enrichProperties()).toMatchObject({ foo: 'bar' })
+      expect(posthog.getPersistedProperty(PostHogPersistedProperty.Props)).toEqual({ foo: 'bar' })
+      posthog.register({ foo2: 'bar2' })
+      expect(posthog.enrichProperties()).toMatchObject({ foo: 'bar', foo2: 'bar2' })
+      expect(posthog.getPersistedProperty(PostHogPersistedProperty.Props)).toEqual({ foo: 'bar', foo2: 'bar2' })
+    })
+
+    it('should unregister properties from storage', () => {
+      posthog.register({ foo: 'bar', foo2: 'bar2' })
+      posthog.unregister('foo')
+      expect(posthog.enrichProperties().foo).toBeUndefined()
+      expect(posthog.enrichProperties().foo2).toEqual('bar2')
+      expect(posthog.getPersistedProperty(PostHogPersistedProperty.Props)).toEqual({ foo2: 'bar2' })
+    })
+
+    it('should register properties only for the session', () => {
+      posthog.registerForSession({ foo: 'bar' })
+      expect(posthog.enrichProperties()).toMatchObject({ foo: 'bar' })
+      expect(posthog.getPersistedProperty(PostHogPersistedProperty.Props)).toEqual(undefined)
+
+      posthog.register({ foo: 'bar2' })
+      expect(posthog.enrichProperties()).toMatchObject({ foo: 'bar' })
+      posthog.unregisterForSession('foo')
+      expect(posthog.enrichProperties()).toMatchObject({ foo: 'bar2' })
+    })
+  })
+})

posthog-react-native/CHANGELOG.md

@@ -1,3 +1,7 @@
+# 2.7.0 - 2023-05-25
+
+1. The `$screen_name` property will be registered for all events whenever `screen` is called
+
 # 2.7.0 - 2023-04-20
 
 1. Fixes a race condition that could occur when initialising PostHog

posthog-react-native/package.json

@@ -1,6 +1,6 @@
 {
   "name": "posthog-react-native",
-  "version": "2.7.0",
+  "version": "2.7.1",
   "main": "lib/posthog-react-native/index.js",
   "files": [
     "lib/"

posthog-react-native/src/posthog-rn.ts

@@ -146,6 +146,11 @@ export class PostHog extends PostHogCore {
 
   // Custom methods
   screen(name: string, properties?: any): this {
+    // Screen name is good to know for all other subsequent events
+    this.registerForSession({
+      $screen_name: name,
+    })
+
     return this.capture('$screen', {
       ...properties,
       $screen_name: name,

posthog-react-native/test/init.spec.ts → posthog-react-native/test/posthog.spec.ts

@@ -1,3 +1,4 @@
+import { PostHogPersistedProperty } from 'posthog-core'
 import { PostHog, PostHogCustomAsyncStorage } from '../index'
 
 describe('PostHog React Native', () => {
@@ -136,4 +137,21 @@ describe('PostHog React Native', () => {
 
     await otherPostHog.shutdownAsync()
   })
+
+  describe('screen', () => {
+    it('should set a $screen_name property on screen', async () => {
+      posthog = await PostHog.initAsync('test-token', {
+        customAsyncStorage: mockStorage,
+        flushInterval: 0,
+      })
+
+      posthog.screen('test-screen')
+
+      expect(posthog.enrichProperties()).toMatchObject({
+        $screen_name: 'test-screen',
+      })
+
+      expect(posthog.getPersistedProperty(PostHogPersistedProperty.Props)).toEqual(undefined)
+    })
+  })
 })