GTM dataLayer Patterns That Survive a Replatform

Flat dataLayer keys become unmanageable past a dozen events. Nest them.

dataLayer.push({
  event: 'transaction_completed',
  transaction: {
    id: 'txn_123',
    amount: 1200,
    currency: 'BDT',
    type: 'p2p',
    sender_id_hash: 'sha256:...',
    recipient_id_hash: 'sha256:...'
  }
});

In GTM, read with a single Data Layer Variable transaction and project sub-fields with Custom JavaScript variables.

SPAs need an explicit page_view push on every route change. Don't rely on the History Change trigger alone — it fires before your route component has populated dataLayer.

// In your router's onRouteChange:
dataLayer.push({
  event: 'page_view',
  page: {
    path: location.pathname,
    title: document.title,
    section: deriveSection(location.pathname)
  }
});

Send amounts in the minor unit (cents/paisa) and the currency code separately. Future-you will thank present-you when you start reporting in multiple currencies.

Don't dataLayer = [] mid-session — GTM will lose its history. On logout, reset only user-scoped keys: dataLayer.push({ user: null }).

Phone numbers, emails, national IDs: hash with SHA-256 in your application code, push the hash. This is non-negotiable in regulated environments.

Add schema_version: 2 to every event. When you change a field, bump the version and keep both readers in GTM for a quarter. This is how you replatform without losing reporting continuity.