Tag add_to_cart properly
The merge trap
The GTM dataLayer does not replace objects: it deep-merges them. An
add_to_cart pushed after a view_item_list therefore inherits the list's
items unless something clears them in between.
The fix is one line, and it must precede every ecommerce event:
dataLayer.push({ ecommerce: null });
dataLayer.push({ event: "add_to_cart", ecommerce: { /* … */ } });That is what pushEcommerce does on this site, and it is its only reason to
exist.
Checking it
On the catalogue, click "Add to cart" on any product. In preview, the
add_to_cart event must carry one item, and its quantity must be 1.
Start again from a product page with the
quantity set to 3. The pushed quantity must be 3, and value 36 — not 12.
select_item is not a click on "Add"
On this site, select_item only fires on a card's link, never on its add button.
The distinction is not cosmetic: counting direct adds as selections inflates the
click-through rate of lists, and the report then shows selections that no product
view follows — an anomaly people spend hours chasing on the attribution side when
it lives on the tagging side.