chore(flags): Add new debugging property $feature_flag_bootstrapped_response and $feature_flag_bootstrapped_payload to $feature_flag_called event

posthog-core/src/index.ts

@@ -777,6 +777,8 @@ export abstract class PostHogCore extends PostHogCoreStateless {
         )
 
       if (Object.keys(bootstrapFlags).length) {
+        this.setPersistedProperty(PostHogPersistedProperty.BootstrapFeatureFlags, bootstrapFlags)
+
         const currentFlags =
           this.getPersistedProperty<PostHogDecideResponse['featureFlags']>(PostHogPersistedProperty.FeatureFlags) || {}
         const newFeatureFlags = { ...bootstrapFlags, ...currentFlags }
@@ -785,6 +787,8 @@ export abstract class PostHogCore extends PostHogCoreStateless {
 
       const bootstrapFlagPayloads = bootstrap.featureFlagPayloads
       if (bootstrapFlagPayloads && Object.keys(bootstrapFlagPayloads).length) {
+        this.setPersistedProperty(PostHogPersistedProperty.BootstrapFeatureFlagPayloads, bootstrapFlagPayloads)
+
         const currentFlagPayloads =
           this.getPersistedProperty<PostHogDecideResponse['featureFlagPayloads']>(
             PostHogPersistedProperty.FeatureFlagPayloads
@@ -1190,6 +1194,8 @@ export abstract class PostHogCore extends PostHogCoreStateless {
                 Object.entries(newFeatureFlagPayloads || {}).map(([k, v]) => [k, this._parsePayload(v)])
               )
             )
+            // Mark that we hit the /decide endpoint so we can capture this in the $feature_flag_called event
+            this.setPersistedProperty(PostHogPersistedProperty.DecideEndpointWasHit, true)
 
             const sessionReplay = res?.sessionRecording
             if (sessionReplay) {
@@ -1252,6 +1258,14 @@ export abstract class PostHogCore extends PostHogCoreStateless {
       this.capture('$feature_flag_called', {
         $feature_flag: key,
         $feature_flag_response: response,
+        $feature_flag_bootstrapped_response: this.getPersistedProperty<PostHogDecideResponse['featureFlags']>(
+          PostHogPersistedProperty.BootstrapFeatureFlags
+        )?.[key],
+        $feature_flag_bootstrapped_payload: this.getPersistedProperty<PostHogDecideResponse['featureFlagPayloads']>(
+          PostHogPersistedProperty.BootstrapFeatureFlagPayloads
+        )?.[key],
+        // If we haven't yet received a response from the /decide endpoint, we must have used the bootstrapped value
+        $used_bootstrap_value: !this.getPersistedProperty(PostHogPersistedProperty.DecideEndpointWasHit),
       })
     }
 

posthog-core/src/types.ts

@@ -49,6 +49,8 @@ export enum PostHogPersistedProperty {
   Props = 'props',
   FeatureFlags = 'feature_flags',
   FeatureFlagPayloads = 'feature_flag_payloads',
+  BootstrapFeatureFlags = 'bootstrap_feature_flags',
+  BootstrapFeatureFlagPayloads = 'bootstrap_feature_flag_payloads',
   OverrideFeatureFlags = 'override_feature_flags',
   Queue = 'queue',
   OptedOut = 'opted_out',
@@ -59,6 +61,7 @@ export enum PostHogPersistedProperty {
   InstalledAppBuild = 'installed_app_build', // only used by posthog-react-native
   InstalledAppVersion = 'installed_app_version', // only used by posthog-react-native
   SessionReplay = 'session_replay', // only used by posthog-react-native
+  DecideEndpointWasHit = 'decide_endpoint_was_hit', // only used by posthog-react-native
 }
 
 export type PostHogFetchOptions = {

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

@@ -407,6 +407,7 @@ describe('PostHog Core', () => {
                 $feature_flag: 'feature-1',
                 $feature_flag_response: true,
                 '$feature/feature-1': true,
+                $used_bootstrap_value: false,
               },
               type: 'capture',
             },
@@ -432,6 +433,7 @@ describe('PostHog Core', () => {
                 $feature_flag: 'feature-1',
                 $feature_flag_response: true,
                 '$feature/feature-1': true,
+                $used_bootstrap_value: false,
               },
               type: 'capture',
             },
@@ -453,6 +455,7 @@ describe('PostHog Core', () => {
                 $feature_flag: 'feature-1',
                 $feature_flag_response: true,
                 '$feature/feature-1': true,
+                $used_bootstrap_value: false,
               },
               type: 'capture',
             },
@@ -501,35 +504,35 @@ describe('PostHog Core', () => {
     })
   })
 
-  describe('bootstapped feature flags', () => {
+  describe('bootstrapped feature flags', () => {
     beforeEach(() => {
       ;[posthog, mocks] = createTestClient(
         'TEST_API_KEY',
         {
           flushAt: 1,
           bootstrap: {
             distinctId: 'tomato',
-            featureFlags: { 'bootstrap-1': 'variant-1', enabled: true, disabled: false },
+            featureFlags: {
+              'bootstrap-1': 'variant-1',
+              'feature-1': 'feature-1-bootstrap-value',
+              enabled: true,
+              disabled: false,
+            },
             featureFlagPayloads: {
               'bootstrap-1': {
                 some: 'key',
               },
+              'feature-1': {
+                color: 'feature-1-bootstrap-color',
+              },
               enabled: 200,
             },
           },
         },
         (_mocks) => {
           _mocks.fetch.mockImplementation((url) => {
             if (url.includes('/decide/')) {
-              return Promise.resolve({
-                status: 200,
-                text: () => Promise.resolve('ok'),
-                json: () =>
-                  Promise.resolve({
-                    featureFlags: createMockFeatureFlags(),
-                    featureFlagPayloads: createMockFeatureFlagPayloads(),
-                  }),
-              })
+              return Promise.reject(new Error('Not responding to emulate use of bootstrapped values'))
             }
 
             return Promise.resolve({
@@ -545,19 +548,48 @@ describe('PostHog Core', () => {
       )
     })
 
-    it('getFeatureFlags should return bootstrapped flags', () => {
-      expect(posthog.getFeatureFlags()).toEqual({ 'bootstrap-1': 'variant-1', enabled: true })
+    it('getFeatureFlags should return bootstrapped flags', async () => {
+      expect(posthog.getFeatureFlags()).toEqual({
+        'bootstrap-1': 'variant-1',
+        enabled: true,
+        'feature-1': 'feature-1-bootstrap-value',
+      })
       expect(posthog.getDistinctId()).toEqual('tomato')
       expect(posthog.getAnonymousId()).toEqual('tomato')
     })
 
-    it('getFeatureFlag should return bootstrapped flags', () => {
+    it('getFeatureFlag should return bootstrapped flags', async () => {
       expect(posthog.getFeatureFlag('my-flag')).toEqual(false)
       expect(posthog.getFeatureFlag('bootstrap-1')).toEqual('variant-1')
       expect(posthog.getFeatureFlag('enabled')).toEqual(true)
       expect(posthog.getFeatureFlag('disabled')).toEqual(false)
     })
 
+    it('getFeatureFlag should capture $feature_flag_called with bootstrapped values', async () => {
+      expect(posthog.getFeatureFlag('bootstrap-1')).toEqual('variant-1')
+
+      await waitForPromises()
+      expect(mocks.fetch).toHaveBeenCalledTimes(1)
+
+      expect(parseBody(mocks.fetch.mock.calls[0])).toMatchObject({
+        batch: [
+          {
+            event: '$feature_flag_called',
+            distinct_id: posthog.getDistinctId(),
+            properties: {
+              $feature_flag: 'bootstrap-1',
+              $feature_flag_response: 'variant-1',
+              '$feature/bootstrap-1': 'variant-1',
+              $feature_flag_bootstrapped_response: 'variant-1',
+              $feature_flag_bootstrapped_payload: { some: 'key' },
+              $used_bootstrap_value: true,
+            },
+            type: 'capture',
+          },
+        ],
+      })
+    })
+
     it('isFeatureEnabled should return true/false for bootstrapped flags', () => {
       expect(posthog.isFeatureEnabled('my-flag')).toEqual(false)
       expect(posthog.isFeatureEnabled('bootstrap-1')).toEqual(true)
@@ -575,6 +607,55 @@ describe('PostHog Core', () => {
 
     describe('when loaded', () => {
       beforeEach(() => {
+        ;[posthog, mocks] = createTestClient(
+          'TEST_API_KEY',
+          {
+            flushAt: 1,
+            bootstrap: {
+              distinctId: 'tomato',
+              featureFlags: {
+                'bootstrap-1': 'variant-1',
+                'feature-1': 'feature-1-bootstrap-value',
+                enabled: true,
+                disabled: false,
+              },
+              featureFlagPayloads: {
+                'bootstrap-1': {
+                  some: 'key',
+                },
+                'feature-1': {
+                  color: 'feature-1-bootstrap-color',
+                },
+                enabled: 200,
+              },
+            },
+          },
+          (_mocks) => {
+            _mocks.fetch.mockImplementation((url) => {
+              if (url.includes('/decide/')) {
+                return Promise.resolve({
+                  status: 200,
+                  text: () => Promise.resolve('ok'),
+                  json: () =>
+                    Promise.resolve({
+                      featureFlags: createMockFeatureFlags(),
+                      featureFlagPayloads: createMockFeatureFlagPayloads(),
+                    }),
+                })
+              }
+
+              return Promise.resolve({
+                status: 200,
+                text: () => Promise.resolve('ok'),
+                json: () =>
+                  Promise.resolve({
+                    status: 'ok',
+                  }),
+              })
+            })
+          }
+        )
+
         posthog.reloadFeatureFlags()
       })
 
@@ -626,6 +707,31 @@ describe('PostHog Core', () => {
         })
         expect(posthog.getFeatureFlagPayload('feature-variant')).toEqual([5])
       })
+
+      it('should capture $feature_flag_called with bootstrapped values', async () => {
+        expect(posthog.getFeatureFlag('feature-1')).toEqual(true)
+
+        await waitForPromises()
+        expect(mocks.fetch).toHaveBeenCalledTimes(2)
+
+        expect(parseBody(mocks.fetch.mock.calls[1])).toMatchObject({
+          batch: [
+            {
+              event: '$feature_flag_called',
+              distinct_id: posthog.getDistinctId(),
+              properties: {
+                $feature_flag: 'feature-1',
+                $feature_flag_response: true,
+                '$feature/feature-1': true,
+                $feature_flag_bootstrapped_response: 'feature-1-bootstrap-value',
+                $feature_flag_bootstrapped_payload: { color: 'feature-1-bootstrap-color' },
+                $used_bootstrap_value: false,
+              },
+              type: 'capture',
+            },
+          ],
+        })
+      })
     })
   })
 

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

@@ -22,7 +22,7 @@ describe('PostHog Core', () => {
       expect(mocks.fetch).toHaveBeenCalledTimes(1)
     })
 
-    it.only('respects timeout', async () => {
+    it('respects timeout', async () => {
       mocks.fetch.mockImplementation(async () => {
         await new Promise((resolve) => setTimeout(resolve, 1000))
         console.log('FETCH RETURNED')

posthog-react-native/CHANGELOG.md

@@ -1,5 +1,9 @@
 # Next
 
+# 3.6.0 - 2024-12-12
+
+1. Add new debugging property `$feature_flag_bootstrapped_response`, `$feature_flag_bootstrapped_payload` and `$used_bootstrap_value` to `$feature_flag_called` event
+
 # 3.5.0 - 2024-12-03
 
 1. fix: deprecate maskPhotoLibraryImages due to unintended masking issues

posthog-react-native/package.json

@@ -1,6 +1,6 @@
 {
   "name": "posthog-react-native",
-  "version": "3.5.0",
+  "version": "3.6.0",
   "main": "lib/posthog-react-native/index.js",
   "files": [
     "lib/"

posthog-web/CHANGELOG.md

@@ -1,5 +1,12 @@
 # Next
 
+# 3.2.0 - 2024-12-12
+
+## Changed
+
+1. Add new debugging property `$feature_flag_bootstrapped_response`, `$feature_flag_bootstrapped_payload` and `$used_bootstrap_value` to `$feature_flag_called` event
+
+
 # 3.1.0 - 2024-11-21
 
 ## Changed

posthog-web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "posthog-js-lite",
-  "version": "3.1.0",
+  "version": "3.2.0",
   "main": "lib/index.cjs.js",
   "module": "lib/index.esm.js",
   "types": "lib/index.d.ts",