PostHog Upgrade & Migration

Current State

!

npm list posthog-js posthog-node 2>/dev/null | grep posthog || echo 'No PostHog SDK found'

Overview

Upgrade posthog-js and posthog-node SDKs safely. Covers version compatibility, breaking changes between major versions (notably the v5 sendFeatureFlags change in posthog-node), and a systematic upgrade procedure.

Prerequisites

• PostHog SDK currently installed
• Git for branching
• Test suite covering PostHog integration
• Staging environment for validation

Instructions

Step 1: Audit Current Versions

set -euo pipefail
# Check installed versions
echo "=== posthog-js ==="
npm list posthog-js 2>/dev/null || echo "Not installed"
echo "=== posthog-node ==="
npm list posthog-node 2>/dev/null || echo "Not installed"
echo "=== Python posthog ==="
pip3 show posthog 2>/dev/null | grep Version || echo "Not installed"

# Check latest available versions
echo "=== Latest available ==="
npm view posthog-js version 2>/dev/null
npm view posthog-node version 2>/dev/null

Step 2: Review Breaking Changes

posthog-node v5.x Breaking Changes:

// BREAKING: sendFeatureFlags no longer automatic with local evaluation
// Before v5.5.0: feature flags auto-sent with events when using local evaluation
// After v5.5.0: must explicitly set sendFeatureFlags: true

// Before (implicit, worked in v4.x)
posthog.capture({
  distinctId: 'user-1',
  event: 'page_viewed',
  // Feature flags were automatically included
});

// After (v5.5.0+, explicit required)
posthog.capture({
  distinctId: 'user-1',
  event: 'page_viewed',
  sendFeatureFlags: true, // Must be explicit now
});

posthog-js Recent Changes:

// Autocapture configuration moved to object format
// Before:
posthog.init('phc_...', { autocapture: true });

// Current: Fine-grained autocapture control
posthog.init('phc_...', {
  autocapture: {
    dom_event_allowlist: ['click', 'submit'],
    element_allowlist: ['a', 'button', 'form', 'input'],
    css_selector_allowlist: ['.track-click'],
    url_ignorelist: ['/health', '/api/internal'],
  },
});

// before_send replaces older event filtering approaches
posthog.init('phc_...', {
  before_send: (event) => {
    // Return null to drop event, or modified event
    if (event.event === '$pageview' && event.properties?.$current_url?.includes('/admin')) {
      return null; // Don't track admin pages
    }
    return event;
  },
});

Step 3: Upgrade Procedure

set -euo pipefail
# Create upgrade branch
git checkout -b upgrade/posthog-sdks

# Upgrade posthog-node
npm install posthog-node@latest
# Check for type errors
npx tsc --noEmit 2>&1 | grep -i posthog || echo "No PostHog type errors"

# Upgrade posthog-js
npm install posthog-js@latest
# Check for type errors
npx tsc --noEmit 2>&1 | grep -i posthog || echo "No PostHog type errors"

# Run tests
npm test

# If Python
pip install --upgrade posthog

Step 4: Search for Deprecated Patterns

set -euo pipefail
# Find files using PostHog
grep -rn "posthog\|PostHog" --include="*.ts" --include="*.tsx" --include="*.js" src/ | \
  grep -v node_modules | grep -v ".d.ts"

# Check for patterns that may need updating
echo "=== Checking for deprecated patterns ==="

# Old import style (posthog-node v3 and earlier)
grep -rn "from 'posthog-node'" --include="*.ts" src/ && echo "Import style: current" || true

# Direct API key in code (should be env var)
grep -rn "phc_\|phx_" --include="*.ts" --include="*.tsx" src/ && \
  echo "WARNING: Hardcoded API key found" || echo "No hardcoded keys"

# Check for sendFeatureFlags usage
grep -rn "sendFeatureFlags" --include="*.ts" src/ || \
  echo "NOTE: No explicit sendFeatureFlags — verify if needed after v5.5.0 upgrade"

Step 5: Validate in Staging

// Post-upgrade validation script
import { PostHog } from 'posthog-node';

async function validateUpgrade() {
  const ph = new PostHog(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
    host: 'https://us.i.posthog.com',
    personalApiKey: process.env.POSTHOG_PERSONAL_API_KEY,
  });

  const checks = {
    capture: false,
    flags: false,
    identify: false,
  };

  try {
    // Test capture
    ph.capture({ distinctId: 'upgrade-test', event: 'sdk_upgrade_validated' });
    checks.capture = true;

    // Test feature flags
    const flags = await ph.getAllFlags('upgrade-test');
    checks.flags = typeof flags === 'object';

    // Test identify
    ph.identify({ distinctId: 'upgrade-test', properties: { upgraded: true } });
    checks.identify = true;

    await ph.flush();
  } catch (error) {
    console.error('Validation failed:', error);
  } finally {
    await ph.shutdown();
  }

  console.log('Upgrade validation:', checks);
  const allPassed = Object.values(checks).every(Boolean);
  process.exit(allPassed ? 0 : 1);
}

validateUpgrade();

Step 6: Rollback if Needed

set -euo pipefail
# Pin to previous version
npm install posthog-node@4.2.1 --save-exact
npm install posthog-js@1.150.0 --save-exact

# Verify rollback
npm test

Version Compatibility

sendFeatureFlags

sendFeatureFlags

before_send

Error Handling

sendFeatureFlags: true

Output

• Upgraded PostHog SDK to latest version
• Deprecated patterns identified and fixed
• All tests passing with new version
• Rollback procedure documented

Resources

• posthog-node Changelog
• posthog-js Changelog
• PostHog Migration Guides

Next Steps

For CI integration during upgrades, see

posthog-ci-integration