GTM Custom HTML Tag: Send purchase event data + first-party cookie attribution (dnm_src/dnm_cid) to Umami via umami.track(). Cookie-less attribution debugging alongside GA4.

gtm-umami-purchase-bridge.js

/**
 * GTM Custom HTML Tag — Umami purchase event bridge
 * File: gtm-umami-purchase-bridge.js
 *
 * What it does:
 *   Sends purchase event data + first-party cookie attribution
 *   to Umami via umami.track(). Runs alongside GA4 purchase tag
 *   to create an independent, cookie-less attribution record.
 *
 * Parameters sent to Umami:
 *   transaction_id  → e.g. "ORD-2026-1234"
 *   value           → e.g. 1250.00
 *   currency        → e.g. "TRY"
 *   ft_source       → e.g. "google"       (from dnm_src cookie)
 *   ft_medium       → e.g. "cpc"          (from dnm_src cookie)
 *   ft_campaign     → e.g. "TR_branded"   (from dnm_src cookie)
 *   ft_click_id     → e.g. "gclid:Cj0K..." (from dnm_cid cookie)
 *
 * Requires:
 *   - Umami script loaded on page (umami.track must be available)
 *   - storageHelper (see companion gist) loaded BEFORE this tag
 *   - ecommerce dataLayer push with transaction_id, value, currency
 *
 * Trigger:
 *   Purchase event trigger (same as GA4 purchase tag).
 *   Tag Sequencing: after storageHelper.
 *   Consent condition: analytics_storage = granted.
 *
 * Fails silently if Umami script is blocked (ad blocker)
 * or not yet loaded.
 */

(function () {
  if (typeof umami === "undefined" || typeof umami.track !== "function") {
    return;
  }

  /* --- 1. Read ecommerce data from dataLayer ---------------------- */
  var dl = window.dataLayer || [];
  var ecomm = null;

  for (var i = dl.length - 1; i >= 0; i--) {
    if (dl[i].ecommerce && dl[i].ecommerce.transaction_id) {
      ecomm = dl[i].ecommerce;
      break;
    }
  }

  var transactionId = ecomm ? String(ecomm.transaction_id) : "";
  var value = ecomm ? Number(ecomm.value) || 0 : 0;
  var currency = ecomm ? String(ecomm.currency || "TRY") : "TRY";

  /* --- 2. Read first-party cookie attribution --------------------- */
  var rawSource = storageHelper.get("dnm_src");
  var rawCid = storageHelper.get("dnm_cid");

  var parts = rawSource ? String(rawSource).split("|") : [];
  var ftSource = parts[0] || "(not set)";
  var ftMedium = parts[1] || "(not set)";
  var ftCampaign = parts[2] || "(not set)";
  var ftClickId = rawCid ? String(rawCid) : "(not set)";

  /* --- 3. Send to Umami ------------------------------------------- */
  umami.track("purchase", {
    transaction_id: transactionId,
    value: value,
    currency: currency,
    ft_source: ftSource,
    ft_medium: ftMedium,
    ft_campaign: ftCampaign,
    ft_click_id: ftClickId,
  });

  /* --- 4. Debug log ----------------------------------------------- */
  if (window.location.search.indexOf("dnm_debug=1") !== -1) {
    console.group("[DNM] Umami purchase bridge");
    console.log("transaction_id :", transactionId);
    console.log("value          :", value, currency);
    console.log("ft_source      :", ftSource);
    console.log("ft_medium      :", ftMedium);
    console.log("ft_campaign    :", ftCampaign);
    console.log("ft_click_id    :", ftClickId);
    console.groupEnd();
  }
})();