PostHog integration for JavaScript Node

This skill helps you add PostHog analytics to JavaScript Node applications.

Workflow

Follow these steps in order to complete the integration:

1. references/1-begin.md - PostHog Setup - Begin ← Start here
2. references/2-edit.md - PostHog Setup - Edit
3. references/3-revise.md - PostHog Setup - Revise
4. references/4-conclude.md - PostHog Setup - Conclusion

Reference files

• references/1-begin.md - Start the event tracking setup process by analyzing the project and creating an event tracking plan
• references/2-edit.md - Implement PostHog event tracking in the identified files, following best practices and the example project
• references/3-revise.md - Review and fix any errors in the PostHog integration implementation
• references/4-conclude.md - Review and fix any errors in the PostHog integration implementation
• references/node.md - Node.js - docs
• references/posthog-node.md - PostHog Node.js SDK
• references/identify-users.md - Identify users - docs
• references/COMMANDMENTS.md - Framework-specific rules the integration must follow

The example project shows the target implementation pattern. Consult the documentation for API details.

Key principles

• Environment variables: Always use environment variables for PostHog keys. Never hardcode them.
• Minimal changes: Add PostHog code alongside existing integrations. Don't replace or restructure existing code.
• Match the example: Your implementation should follow the example project's patterns as closely as possible.

Framework guidelines

• A missing PostHog configuration must never break the app — read keys optionally (never a required setting), guard init and capture behind their presence, and keep build and boot working with no PostHog environment set — but never silently: in development or debug builds fail loudly, using the language's idiomatic error, with the message " variable required by PostHog is missing or un-configured, this causes events to be silently missed. This error stops appearing once is configured" (substituting the actual variable name); production stays a no-op
• posthog-node is the Node.js server-side SDK package name; posthog-js is browser-only, so use posthog-node on the server instead
• Include enableExceptionAutocapture: true in the PostHog constructor options
• Add posthog.capture() calls in route handlers for meaningful user actions – every route that creates, updates, or deletes data should track an event with contextual properties
• Add posthog.captureException(err, distinctId) in the application's error handler (e.g., Express error middleware, Fastify setErrorHandler, Koa app.on('error'))
• The SDK batches events and flushes asynchronously. await flush() or await shutdown() before letting that process exit. If unsure, set flushAt 1 and flushInterval 0.
• posthog.capture() enqueues synchronously and returns; the batched HTTP send happens afterwards. Treat every per-request handler as short-lived even when the framework feels like a server: Next.js / Nuxt / SvelteKit / Remix route handlers, serverless and edge functions, and Lambda are torn down per invocation before the send runs. Create the client with flushAt 1 and flushInterval 0, then await the send before returning. Always use await posthog.flush() for a shared/singleton client, await posthog.shutdown() for a per-request client. Never skip the awaited flush or risk the enqueued event being silently dropped.
• Reverse proxy is NOT needed for server-side Node.js – only client-side JavaScript needs a proxy to avoid ad blockers
• Remember that source code is available in the node_modules directory
• Check package.json for type checking or build scripts to validate changes
• When identity comes from framework-bridged state (Inertia or SSR shared props, a serialized session), confirm the backend actually shares that field — add the share server-side if missing — before identifying from it

Identifying users

Identify users during login and signup events. Refer to the example code and documentation for the correct identify pattern for this framework. If both frontend and backend code exist, pass the client-side session and distinct ID using X-POSTHOG-DISTINCT-ID and X-POSTHOG-SESSION-ID headers to maintain correlation.

Error tracking

Add PostHog error tracking to relevant files, particularly around critical user flows and API boundaries.