[Feature Request] GTM DataLayer integration — E-commerce event tracking for storefronts

[lucianfialho]

Problem

The analytics module (added in #12505) provides a backend-only provider interface with track() and identify() methods. However:

1. No automatic event tracking — No subscribers or workflow hooks call track() on commerce events (order.placed, cart.updated, etc.). The PostHog provider exists but is effectively unused without custom code.
2. No frontend tracking support — The analytics module is server-side only (Node.js). There's no mechanism for browser-side event tracking, which is where most e-commerce analytics tools operate.
3. No GTM/GA4 integration — Google Tag Manager is the industry standard for e-commerce tracking. Platforms like Shopify, WooCommerce, and BigCommerce all provide built-in GTM dataLayer support with GA4 e-commerce events.

Proposal

A lightweight frontend package (@medusajs/gtm-datalayer or similar) that:

1. Injects the GTM snippet

import { MedusaGTM } from "@medusajs/gtm-datalayer"
const gtm = new MedusaGTM({ containerId: "GTM-XXXXX" })
gtm.install()

2. Maps Medusa data to GA4 e-commerce dataLayer events

Storefront action	GA4 dataLayer event	Data mapped
Product list rendered	view_item_list	products → items[]
Product page loaded	view_item	variant price, categories, brand
Add line item to cart	add_to_cart	unit_price/100, quantity
Remove line item	remove_from_cart	same
View cart	view_cart	cart total, all items
Start checkout	begin_checkout	cart + coupon
Select shipping	add_shipping_info	shipping_tier
Select payment	add_payment_info	payment_type
Order confirmed	purchase	transaction_id, totals, tax, shipping
Return processed	refund	order_id, refunded items

3. Handles Medusa-specific details

• Converts amounts from cents to currency units (Medusa stores in smallest unit)
• Maps product categories hierarchy to item_category / item_category2 / etc.
• Maps variant options to item_variant
• Clears ecommerce object before each push (required by GTM)

Why GTM instead of direct GA4?

GTM is a multiplexer — the merchant configures their container once in Medusa, and from GTM they can route events to GA4, Meta Pixel, TikTok, Pinterest, Google Ads conversions, and any other tool, all without code changes. This is how it works on Shopify, WooCommerce, and every major e-commerce platform.

Scope

This could start as:

• External package — no core changes needed, works with any Medusa storefront
• Framework-agnostic — vanilla JS with optional React hooks
• Typed — full TypeScript with Medusa's HttpTypes for product/cart/order mapping

I'm available to implement and test this.

Would love feedback on:

1. Should this live in the monorepo (as a new package under packages/) or as a community package?
2. Is there interest in also wiring automatic track() calls via subscribers for the existing backend analytics module?
3. Should the GTM container ID be configurable via store metadata in the admin panel, or just passed as a config option?