feat: Add Event Timer module

src/EventTimer.ts

@@ -0,0 +1,102 @@
+class Event {
+	name: string;
+	ts: DOMHighResTimeStamp;
+
+	constructor(name: string, mark: PerformanceEntry) {
+		this.name = name;
+		this.ts = mark.startTime;
+	}
+}
+
+interface SlotEventStatus {
+	prebidStart: boolean;
+	prebidEnd: boolean;
+	slotInitalised: boolean;
+	adOnPage: boolean;
+}
+
+export class EventTimer {
+	events: Event[];
+	startTS: DOMHighResTimeStamp;
+	triggers: {
+		first: SlotEventStatus;
+		'top-above-nav': SlotEventStatus;
+	};
+
+	/**
+	 * Initalise the EventTimer class on page.
+	 * Returns a singleton instance of the EventTimer class and binds
+	 * to window.guardian.commercialTimer. If it's been previously
+	 * initalised and bound it returns the original instance
+	 *
+	 * @returns {EventTimer} Instance of EventTimer
+	 */
+	static init(): EventTimer {
+		return (window.guardian.commercialTimer ||= new EventTimer());
+	}
+
+	constructor() {
+		this.events = [];
+		this.startTS = performance.now();
+		this.triggers = {
+			first: {
+				prebidStart: false,
+				prebidEnd: false,
+				slotInitalised: false,
+				adOnPage: false,
+			},
+			'top-above-nav': {
+				prebidStart: false,
+				prebidEnd: false,
+				slotInitalised: false,
+				adOnPage: false,
+			},
+		};
+	}
+
+	mark(name: string): PerformanceEntry {
+		const longName = `gu.commercial.${name}`;
+		performance.mark(longName);
+
+		// Most recent mark with this name is the event we just created.
+		const mark = performance
+			.getEntriesByName(longName, 'mark')
+			.slice(-1)[0];
+		this.events.push(new Event(name, mark));
+		return mark;
+	}
+
+	/**
+	 * Creates a new performance mark
+	 * For slot events also ensures each TYPE of event event is marked only once for 'first'
+	 * (the first time that event is triggered for ANY slot) and once for topAboveNav
+	 *
+	 * @param {string} eventName - The short name applied to the mark
+	 * @param {origin} [origin=page] - Either 'page' (default) or the name of the slot
+	 */
+	trigger(eventName: string, origin = 'page'): void {
+		const TRACKEDSLOTNAME = 'top-above-nav';
+		if (origin === 'page') {
+			this.mark(eventName);
+			return;
+		}
+
+		if (!this.triggers.first[eventName as keyof SlotEventStatus]) {
+			this.mark(`first-{eventName}`);
+			this.triggers.first[eventName as keyof SlotEventStatus] = true;
+		}
+
+		if (origin === TRACKEDSLOTNAME) {
+			if (
+				!this.triggers[TRACKEDSLOTNAME][
+					eventName as keyof SlotEventStatus
+				]
+			) {
+				this.mark(`${TRACKEDSLOTNAME}-{eventName}`);
+				this.triggers[TRACKEDSLOTNAME][
+					eventName as keyof SlotEventStatus
+				] = true;
+			}
+		}
+	}
+}

src/index.ts

@@ -6,4 +6,6 @@ export { fbPixel } from './third-party-tags/facebook-pixel';
 export { twitter } from './third-party-tags/twitter-uwt';
 export { inizio } from './third-party-tags/inizio';
 export { remarketing } from './third-party-tags/remarketing';
+export { EventTimer } from './EventTimer';
+
 export type { ThirdPartyTag } from './types';

src/types.ts

@@ -1,3 +1,5 @@
+import type { EventTimer } from './EventTimer';
+
 export type TagAtrribute = {
 	name: string;
 	value: string;
@@ -34,5 +36,8 @@ declare global {
 			val: Record<string, unknown>;
 		}>;
 		googletag?: googletag.Googletag;
+		guardian: {
+			commercialTimer?: EventTimer;
+		};
 	}
 }