perf: clean up GTM init listeners after first successful initialization

gatsby-browser.js

@@ -5,29 +5,51 @@ import "slick-carousel/slick/slick-theme.css";
 export const disableCorePrefetching = () =>
   process.env.NODE_ENV === "development";
 
+const GTM_DELAY_MS = 3500;
+const GTM_INIT_EVENTS = ["scroll", "mousemove", "touchstart"];
+
+function addInitListeners() {
+  GTM_INIT_EVENTS.forEach((eventName) => {
+    document.addEventListener(eventName, initGTMOnEvent);
+  });
+}
+
+function removeInitListeners() {
+  GTM_INIT_EVENTS.forEach((eventName) => {
+    document.removeEventListener(eventName, initGTMOnEvent);
+  });
+}
+
 document.addEventListener("DOMContentLoaded", () => {
-  /** init gtm after 3500 seconds - this could be adjusted */
-  setTimeout(initGTM, 3500);
+  // Initialize GTM after a short delay unless user interaction triggers it first.
+  setTimeout(initGTM, GTM_DELAY_MS);
 });
-document.addEventListener("scroll", initGTMOnEvent);
-document.addEventListener("mousemove", initGTMOnEvent);
-document.addEventListener("touchstart", initGTMOnEvent);
-function initGTMOnEvent(event) {
+
+addInitListeners();
+
+function initGTMOnEvent() {
   initGTM();
-  event.currentTarget.removeEventListener(event.type, initGTMOnEvent); // remove the event listener that got triggered
 }
+
 function initGTM() {
   if (window.gtmDidInit) {
     return false;
   }
+
   window.gtmDidInit = true; // flag to ensure script does not get added to DOM more than once.
+  removeInitListeners();
+
   const script = document.createElement("script");
   script.type = "text/javascript";
   script.async = true;
   // ensure PageViews is always tracked (on script load)
   script.onload = () => {
     window.dataLayer = window.dataLayer || [];
-    window.dataLayer.push({ event: "gtm.js", "gtm.start": new Date().getTime(), "gtm.uniqueEventId": 0 });
+    window.dataLayer.push({
+      event: "gtm.js",
+      "gtm.start": new Date().getTime(),
+      "gtm.uniqueEventId": 0,
+    });
   };
   script.src = "https://www.googletagmanager.com/gtm.js?id=GTM-PS26QB9";
   document.head.appendChild(script);