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Send analytics events to PostHog alongside GA4 - #165
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Send every tracked event to both GA4 and PostHog so the numbers can be compared for a release before deciding whether to drop GA. - src/js/lib/posthog.js: minimal client posting to PostHog's HTTP capture API (the posthog-js SDK is DOM-oriented and doesn't fit an MV3 service worker). No-ops until a real project API key is pasted in, so this can land before the PostHog project exists. - tracker.js: dual-writes in send() and set(). Reuses the stored GA client_id as the PostHog distinct_id so install continuity would be preserved on a full cutover. Maps page_view -> $pageview and exception -> $exception (with $exception_list) so PostHog's web analytics and error tracking UIs work natively. Events are sent as anonymous ($process_person_profile: false). The Tracker facade and all call sites are unchanged. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011xxfT1FSUpycKgMw8JZ6oS
- rename dimension1/dimension2 to version/channel in the PostHog super properties, since PostHog doesn't share GA's restrictive custom dimension naming, and drop the dimension keys from the PostHog copy - move the exception description into $exception_list instead of duplicating it, since stack traces can be 2000 chars and nothing in PostHog reads the GA-style description property Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011xxfT1FSUpycKgMw8JZ6oS
Analysis of the GA4 numbers shows ~92% of the 32.7M monthly events are MV3 service worker lifecycle noise: the startup page_view and background-loaded timing fire together on every worker wakeup (~33/user/day). Proposes deleting the startup pageview, sampling background-loaded, collapsing the update triplet into one event with numeric properties, replacing the popup-focus pageviews with a popup_open property, and investigating the 555K/month exceptions (starting with registering description as a GA4 custom dimension so the messages are visible). Projected 32.7M -> ~2.5M/month, which also makes PostHog's free tier cover a ~40% user sample instead of ~3%. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011xxfT1FSUpycKgMw8JZ6oS
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October 5, 2026 01:40
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Requested by John · project thread
Before: the PostHog dual-write only existed on
feature/posthog-analytics, which branches offmaster(v2.0.2) and so sits 468 commits behinddev.After: the same change sits on top of the latest
dev. Every tracked event still goes to GA4 and is also posted to PostHog's capture API. PostHog stays a no-op until a realphc_project key replaces the placeholder insrc/js/lib/posthog.js. The analytics streamlining writeup (analytics-proposal.md) comes along too.How: cherry-picked all three commits from
feature/posthog-analytics(c70b443 "Add PostHog analytics alongside GA4…", 57c01a7 "Clean up PostHog property names", and e4d1ca1 "Add analytics event streamlining proposal"). They applied cleanly on top of dev'stracker.jschanges, including the ignored-errors filter from e5e751f, which still returns before anything is sent to either service.Checked:
npm testpasses (22 files, 175 tests) andnpm run build:devsucceeds with the PostHog client indist/dev/js/background.js. Not yet loaded as an unpacked extension or exercised against a real PostHog project.🤖 Generated with Claude Code
https://claude.ai/code/session_013uHCZeugQLw21d4oFhtPRP