meta pixel: more robust loading & graceful failure with adblockers

src/lib/util/meta-pixel-loader.ts

@@ -1,4 +1,5 @@
 import { browser } from '$app/environment';
+import log from 'loglevel';
 
 const SCRIPT_SRC = 'https://connect.facebook.net/en_US/fbevents.js';
 
@@ -18,12 +19,24 @@ type QueuedFBQ = ((...args: unknown[]) => void) & {
 export const loadMetaPixel = (): Promise<void> => {
 	// Make sure we're using the browser
 	if (!browser || !window) {
-		return Promise.reject(new Error('Window is undefined'));
+		return Promise.reject(new Error(`Not in browser, can't access window`));
 	}
 
 	// If fbq is already defined, resolve immediately
 	const existing = window.fbq as QueuedFBQ | undefined;
-	if (existing && existing.loaded) {
+	if (existing) {
+		const existingScript = getExistingScript();
+		if (existingScript) {
+			return new Promise((resolve, reject) => {
+				attachToScript(existingScript, resolve, reject);
+			});
+		}
+
+		log.debug(
+			'Meta Pixel fbq already present, skipping injection',
+			existing.version,
+			existing.queue
+		);
 		return Promise.resolve();
 	}
 
@@ -41,17 +54,14 @@ export const loadMetaPixel = (): Promise<void> => {
 	q.loaded = true;
 	q.version = '2.0';
 	window.fbq = q;
+	window._fbq = q;
 
 	return new Promise((resolve, reject) => {
 		// Avoid adding the same script twice
-		const existingScript = document.querySelector(
-			`script[src="${SCRIPT_SRC}"]`
-		) as HTMLScriptElement | null;
+		const existingScript = getExistingScript();
 		if (existingScript) {
-			existingScript.addEventListener('load', () => resolve());
-			existingScript.addEventListener('error', () =>
-				reject(new Error('Failed to load Meta Pixel script'))
-			);
+			attachToScript(existingScript, resolve, reject);
+			log.debug('Meta Pixel script already present, waiting for load');
 			return;
 		}
 
@@ -59,8 +69,23 @@ export const loadMetaPixel = (): Promise<void> => {
 		const script = document.createElement('script');
 		script.src = SCRIPT_SRC;
 		script.async = true;
-		script.addEventListener('load', () => resolve());
-		script.addEventListener('error', () => reject(new Error('Failed to load Meta Pixel script')));
+		attachToScript(script, resolve, reject);
 		document.head.appendChild(script);
+		log.debug('Meta Pixel script added to document');
 	});
 };
+
+const getExistingScript = (): HTMLScriptElement | null => {
+	return document.querySelector(
+		`script[src*="connect.facebook.net"][src*="fbevents.js"]`
+	) as HTMLScriptElement | null;
+};
+
+const attachToScript = (
+	el: HTMLScriptElement,
+	resolve: () => void,
+	reject: (err: Error) => void
+) => {
+	el.addEventListener('load', () => resolve());
+	el.addEventListener('error', () => reject(new Error('Failed to load Meta Pixel script')));
+};