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feat: track time-on-page via unload ping for accurate visit durations

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Sends duration to the metrics endpoint on visibilitychange and SPA
navigation. Also lowers journey min_sessions to 1 for low-traffic sites.
This commit is contained in:
Usman Baig
2026-03-14 14:07:54 +01:00
parent 11ef95ef45
commit cf0b6b8a68
2 changed files with 30 additions and 9 deletions
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37
public/script.js
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@@ -39,6 +39,9 @@
let clsObserved = false;
let performanceInsightsEnabled = false;
// * Time-on-page tracking: records when the current pageview started
var pageStartTime = 0;
// * Minimal Web Vitals Observer
function observeMetrics() {
try {
@@ -79,16 +82,30 @@
}
function sendMetrics() {
if (!performanceInsightsEnabled || !currentEventId) return;
if (!currentEventId) return;
// * Only include LCP/CLS when the browser actually reported them. Sending 0 overwrites
// * the DB before LCP/CLS have fired (they fire late). The backend does partial updates
// * and leaves unset fields unchanged.
const payload = { event_id: currentEventId, inp: metrics.inp };
if (lcpObserved) payload.lcp = metrics.lcp;
if (clsObserved) payload.cls = metrics.cls;
// * Calculate time-on-page in seconds (always sent, even without performance insights)
var durationSec = pageStartTime > 0 ? Math.round((Date.now() - pageStartTime) / 1000) : 0;
const data = JSON.stringify(payload);
var payload = { event_id: currentEventId };
// * Always include duration if we have a valid measurement
if (durationSec > 0) payload.duration = durationSec;
// * Only include Web Vitals when performance insights are enabled
if (performanceInsightsEnabled) {
payload.inp = metrics.inp;
// * Only include LCP/CLS when the browser actually reported them. Sending 0 overwrites
// * the DB before LCP/CLS have fired (they fire late). The backend does partial updates
// * and leaves unset fields unchanged.
if (lcpObserved) payload.lcp = metrics.lcp;
if (clsObserved) payload.cls = metrics.cls;
}
// * Skip if nothing to send (no duration and no vitals)
if (!payload.duration && !performanceInsightsEnabled) return;
var data = JSON.stringify(payload);
if (navigator.sendBeacon) {
navigator.sendBeacon(apiUrl + '/api/v1/metrics', new Blob([data], {type: 'application/json'}));
@@ -301,7 +318,7 @@
}
if (currentEventId) {
// * SPA nav: visibilitychange may not fire, so send previous page's metrics now
// * SPA nav: visibilitychange may not fire, so send previous page's metrics + duration now
sendMetrics();
}
@@ -309,6 +326,7 @@
lcpObserved = false;
clsObserved = false;
currentEventId = null;
pageStartTime = 0;
// * Only send external referrer on the first pageview (landing page).
// * SPA navigations keep document.referrer stale, so clear it after first hit
// * to avoid inflating traffic source attribution.
@@ -357,6 +375,7 @@
firstPageviewSent = true;
if (data && data.id) {
currentEventId = data.id;
pageStartTime = Date.now();
// * For SPA navigations the browser never emits a new largest-contentful-paint
// * (LCP is only for full document loads). After the new view has had time to
// * paint, we record time-from-route-change as an LCP proxy so /products etc.