Fix session resumption when changing storage strategy with disableAnonymousTracking

common/changes/@snowplow/browser-tracker-core/issue-bcpf-1813-stratchange-resume_2025-05-23-06-07.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@snowplow/browser-tracker-core",
+      "comment": "Resume sessions when disabling anonymous tracking that was already tracking session state",
+      "type": "none"
+    }
+  ],
+  "packageName": "@snowplow/browser-tracker-core"
+}

common/changes/@snowplow/javascript-tracker/issue-bcpf-1813-stratchange-resume_2025-05-23-08-06.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@snowplow/javascript-tracker",
+      "comment": "Resume sessions when disabling anonymous tracking that was already tracking session state",
+      "type": "none"
+    }
+  ],
+  "packageName": "@snowplow/javascript-tracker"
+}

libraries/browser-tracker-core/src/tracker/index.ts

@@ -1379,10 +1379,23 @@ export function Tracker(
       },
 
       disableAnonymousTracking: function (configuration?: DisableAnonymousTrackingConfiguration) {
+        /*
+          Flag for if the state storage strategy has changed and we are currently storing session state (anonymously or not).
+          Because the strategy changes, the below call to initializeIdsAndCookies will fail to see that a session is currently in progress and start a new one.
+          Detect this state, and once we've updated settings, bump the session cookie with the new strategy to ensure it exists before loading the ID cookie, which will resume the session.
+        */
+        const shouldResumeSession =
+          configuration?.stateStorageStrategy && // a new strategy was defined (otherwise will already resume)
+          configuration.stateStorageStrategy !== configStateStorageStrategy && // new strategy is different to old one (otherwise will already resume)
+          (!configAnonymousTracking || configAnonymousSessionTracking) && // we were previously tracking session IDs (otherwise nothing to resume)
+          getSnowplowCookieValue('ses'); // and we currently have a session in progress (otherwise we want a new session anyway)
+
         trackerConfiguration.anonymousTracking = false;
 
         toggleAnonymousTracking(configuration);
 
+        if (shouldResumeSession) setSessionCookie(); // ensure session cookie exists with new strategy
+
         initializeIdsAndCookies();
 
         outQueue.executeQueue(); // There might be some events in the queue we've been unable to send in anonymous mode

trackers/javascript-tracker/test/integration/sessionStorage.test.ts

@@ -181,7 +181,20 @@ describe('Sessions', () => {
           log
         )
       )
-    ).toBe(3);
+    ).toBe(4);
+    expect(
+      F.size(
+        F.uniqBy(
+          F.get('event.domain_sessionid'),
+          F.filter(
+            (e) =>
+              F.get('event.name_tracker', e) === 'anonymousSessionTracker' &&
+              F.get('event.app_id', e) === 'session-integration-' + testIdentifier,
+            log
+          )
+        )
+      )
+    ).toBe(2);
   });
 
   it('should only increment domain_sessionidx outside of session timeout (cookie storage)', () => {

trackers/javascript-tracker/test/pages/session-integration.html

@@ -52,21 +52,25 @@
 
       window.snowplow('newTracker', 'anonymousSessionTracker', collector_endpoint, {
         appId: 'session-integration-' + testIdentifier,
-        cookieName: testIdentifier,
+        cookieName: testIdentifier + 'anon',
         sessionCookieTimeout: 1,
         stateStorageStrategy: 'localStorage',
         anonymousTracking: { withSessionTracking: true },
       });
 
       const currentUrl = window.location.href;
       const url = new URL(currentUrl);
-      if (url.searchParams.has("delayed")) {
+      if (url.searchParams.has('delayed')) {
         setTimeout(function () {
           window.snowplow('trackPageView:cookieSessionTracker');
 
           window.snowplow('trackPageView:localStorageSessionTracker');
 
           window.snowplow('trackPageView:anonymousSessionTracker');
+          window.snowplow('disableAnonymousTracking:anonymousSessionTracker', {
+            stateStorageStrategy: 'cookieAndLocalStorage',
+          });
+          window.snowplow('trackPageView:anonymousSessionTracker');
         }, 0);
       } else {
         setTimeout(function () {
@@ -81,7 +85,7 @@
         }, 0);
 
         setTimeout(function () {
-          url.searchParams.set("delayed", "1");
+          url.searchParams.set('delayed', '1');
           window.location.href = url.toString();
         }, 3000);
       }