From 18c4670ad366c87a0792cde4a08fd6f542df4445 Mon Sep 17 00:00:00 2001
From: Lukas Stracke <lukas.stracke@sentry.io>
Date: Wed, 7 Jan 2026 11:27:34 +0100
Subject: [PATCH] ref(core): Remove dependence between `performance.timeorigin`
 and `performance.timing.navigationStart`

---
 packages/core/src/utils/time.ts           | 37 +++++++++++------------
 packages/core/test/lib/utils/time.test.ts | 25 ---------------
 2 files changed, 17 insertions(+), 45 deletions(-)

diff --git a/packages/core/src/utils/time.ts b/packages/core/src/utils/time.ts
index bfed9386f8bb..202c39da3abe 100644
--- a/packages/core/src/utils/time.ts
+++ b/packages/core/src/utils/time.ts
@@ -78,12 +78,14 @@ let cachedTimeOrigin: number | null | undefined = null;
 
 /**
  * Gets the time origin and the mode used to determine it.
+ *
+ * Unfortunately browsers may report an inaccurate time origin data, through either performance.timeOrigin or
+ * performance.timing.navigationStart, which results in poor results in performance data. We only treat time origin
+ * data as reliable if they are within a reasonable threshold of the current time.
+ *
  * TODO: move to `@sentry/browser-utils` package.
  */
 function getBrowserTimeOrigin(): number | undefined {
-  // Unfortunately browsers may report an inaccurate time origin data, through either performance.timeOrigin or
-  // performance.timing.navigationStart, which results in poor results in performance data. We only treat time origin
-  // data as reliable if they are within a reasonable threshold of the current time.
   const { performance } = GLOBAL_OBJ as typeof GLOBAL_OBJ & Window;
   if (!performance?.now) {
     return undefined;
@@ -94,11 +96,13 @@ function getBrowserTimeOrigin(): number | undefined {
   const performanceNow = performance.now();
   const dateNow = Date.now();
 
-  // if timeOrigin isn't available set delta to threshold so it isn't used
-  const timeOriginDelta = performance.timeOrigin
-    ? Math.abs(performance.timeOrigin + performanceNow - dateNow)
-    : threshold;
-  const timeOriginIsReliable = timeOriginDelta < threshold;
+  const timeOrigin = performance.timeOrigin;
+  if (typeof timeOrigin === 'number') {
+    const timeOriginDelta = Math.abs(timeOrigin + performanceNow - dateNow);
+    if (timeOriginDelta < threshold) {
+      return timeOrigin;
+    }
+  }
 
   // TODO: Remove all code related to `performance.timing.navigationStart` once we drop support for Safari 14.
   // `performance.timeSince` is available in Safari 15.
@@ -111,18 +115,11 @@ function getBrowserTimeOrigin(): number | undefined {
   // Date API.
   // eslint-disable-next-line deprecation/deprecation
   const navigationStart = performance.timing?.navigationStart;
-  const hasNavigationStart = typeof navigationStart === 'number';
-  // if navigationStart isn't available set delta to threshold so it isn't used
-  const navigationStartDelta = hasNavigationStart ? Math.abs(navigationStart + performanceNow - dateNow) : threshold;
-  const navigationStartIsReliable = navigationStartDelta < threshold;
-
-  // TODO: Since timeOrigin explicitly replaces navigationStart, we should probably remove the navigationStartIsReliable check.
-  if (timeOriginIsReliable && timeOriginDelta <= navigationStartDelta) {
-    return performance.timeOrigin;
-  }
-
-  if (navigationStartIsReliable) {
-    return navigationStart;
+  if (typeof navigationStart === 'number') {
+    const navigationStartDelta = Math.abs(navigationStart + performanceNow - dateNow);
+    if (navigationStartDelta < threshold) {
+      return navigationStart;
+    }
   }
 
   // TODO: We should probably fall back to Date.now() - performance.now(), since this is still more accurate than just Date.now() (?)
diff --git a/packages/core/test/lib/utils/time.test.ts b/packages/core/test/lib/utils/time.test.ts
index e40c607cb409..b6db4df1d479 100644
--- a/packages/core/test/lib/utils/time.test.ts
+++ b/packages/core/test/lib/utils/time.test.ts
@@ -77,31 +77,6 @@ describe('browserPerformanceTimeOrigin', () => {
     vi.unstubAllGlobals();
   });
 
-  it('returns `performance.timing.navigationStart` if `performance.timeOrigin` is less reliable', async () => {
-    const currentTimeMs = 1767778040874;
-
-    const navigationStartMs = currentTimeMs - 2_000;
-
-    const timeSincePageloadMs = 1_234.789;
-
-    vi.useFakeTimers();
-    vi.setSystemTime(new Date(currentTimeMs));
-
-    vi.stubGlobal('performance', {
-      timeOrigin: navigationStartMs - 1,
-      timing: {
-        navigationStart: navigationStartMs,
-      },
-      now: () => timeSincePageloadMs,
-    });
-
-    const timeOrigin = await getFreshPerformanceTimeOrigin();
-    expect(timeOrigin).toBe(navigationStartMs);
-
-    vi.useRealTimers();
-    vi.unstubAllGlobals();
-  });
-
   describe('caching', () => {
     it('caches `undefined` result', async () => {
       vi.stubGlobal('performance', undefined);