fix: Use the more reliable timeOrigin (#3398)

* fix: Use the more reliable timeOrigin

- We want to still avoid using date.now() if possible, but this way if
  either or both performance apis are reliable, we use the more reliable
  one instead of still defaulting to timeOrigin

Author: wmak

packages/utils/src/time.ts

@@ -147,13 +147,14 @@ export const browserPerformanceTimeOrigin = ((): number | undefined => {
   }
 
   const threshold = 3600 * 1000;
+  const performanceNow = performance.now();
+  const dateNow = Date.now();
 
-  const timeOriginIsReliable =
-    performance.timeOrigin && Math.abs(performance.timeOrigin + performance.now() - Date.now()) < threshold;
-  if (timeOriginIsReliable) {
-    _browserPerformanceTimeOriginMode = 'timeOrigin';
-    return performance.timeOrigin;
-  }
+  // 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;
 
   // While performance.timing.navigationStart is deprecated in favor of performance.timeOrigin, performance.timeOrigin
   // is not as widely supported. Namely, performance.timeOrigin is undefined in Safari as of writing.
@@ -163,14 +164,22 @@ export const browserPerformanceTimeOrigin = ((): number | undefined => {
   // eslint-disable-next-line deprecation/deprecation
   const navigationStart = performance.timing && performance.timing.navigationStart;
   const hasNavigationStart = typeof navigationStart === 'number';
-  const navigationStartIsReliable =
-    hasNavigationStart && Math.abs(navigationStart + performance.now() - Date.now()) < threshold;
-  if (navigationStartIsReliable) {
-    _browserPerformanceTimeOriginMode = 'navigationStart';
-    return navigationStart;
+  // 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;
+
+  if (timeOriginIsReliable || navigationStartIsReliable) {
+    // Use the more reliable time origin
+    if (timeOriginDelta <= navigationStartDelta) {
+      _browserPerformanceTimeOriginMode = 'timeOrigin';
+      return performance.timeOrigin;
+    } else {
+      _browserPerformanceTimeOriginMode = 'navigationStart';
+      return navigationStart;
+    }
   }
 
   // Either both timeOrigin and navigationStart are skewed or neither is available, fallback to Date.
   _browserPerformanceTimeOriginMode = 'dateNow';
-  return Date.now();
+  return dateNow;
 })();