From ec9cdf1710ae80267ceda921f65bbd3f9845da13 Mon Sep 17 00:00:00 2001
From: Alberto Leal <mail4alberto@gmail.com>
Date: Fri, 16 Oct 2020 16:53:42 -0400
Subject: [PATCH] fix(web-vitals): Only report FCP or FP if the page wasn't
 hidden prior to their instrumentation

---
 packages/tracing/src/browser/metrics.ts | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/packages/tracing/src/browser/metrics.ts b/packages/tracing/src/browser/metrics.ts
index f2830f3ad6eb..bcef09afc79e 100644
--- a/packages/tracing/src/browser/metrics.ts
+++ b/packages/tracing/src/browser/metrics.ts
@@ -10,6 +10,7 @@ import { getCLS } from './web-vitals/getCLS';
 import { getFID } from './web-vitals/getFID';
 import { getLCP } from './web-vitals/getLCP';
 import { getTTFB } from './web-vitals/getTTFB';
+import { getFirstHidden } from './web-vitals/lib/getFirstHidden';
 
 const global = getGlobalObject<Window>();
 
@@ -85,13 +86,17 @@ export class MetricsInstrumentation {
 
             // capture web vitals
 
-            if (entry.name === 'first-paint') {
+            const firstHidden = getFirstHidden();
+            // Only report if the page wasn't hidden prior to the web vital.
+            const shouldRecord = entry.startTime < firstHidden.timeStamp;
+
+            if (entry.name === 'first-paint' && shouldRecord) {
               logger.log('[Measurements] Adding FP');
               this._measurements['fp'] = { value: entry.startTime };
               this._measurements['mark.fp'] = { value: startTimestamp };
             }
 
-            if (entry.name === 'first-contentful-paint') {
+            if (entry.name === 'first-contentful-paint' && shouldRecord) {
               logger.log('[Measurements] Adding FCP');
               this._measurements['fcp'] = { value: entry.startTime };
               this._measurements['mark.fcp'] = { value: startTimestamp };