Function getBrowserTimeOrigin

packages/core/src/utils/time.ts:89–128

* 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 re

()

 * TODO: move to `@sentry/browser-utils` package.
 */
function getBrowserTimeOrigin(): number | undefined {
  const { performance } = GLOBAL_OBJ as typeof GLOBAL_OBJ & Window;
  if (!performance?.now) {
    return undefined;
  }

  const threshold = 300_000; // 5 minutes in milliseconds
  const performanceNow = withRandomSafeContext(() => performance.now());
  const dateNow = safeDateNow();

  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.
  // see: https://caniuse.com/mdn-api_performance_timeorigin

  // 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.
  // Also as of writing, performance.timing is not available in Web Workers in mainstream browsers, so it is not always
  // a valid fallback. In the absence of an initial time provided by the browser, fallback to the current time from the
  // Date API.
  // eslint-disable-next-line typescript/no-deprecated
  const navigationStart = performance.timing?.navigationStart;
  if (typeof navigationStart === 'number') {
    const navigationStartDelta = Math.abs(navigationStart + performanceNow - dateNow);
    if (navigationStartDelta < threshold) {
      return navigationStart;
    }
  }

  // Either both timeOrigin and navigationStart are skewed or neither is available, fallback to subtracting
  // `performance.now()` from `Date.now()`.
  return dateNow - performanceNow;
}

/**
 * The number of milliseconds since the UNIX epoch. This value is only usable in a browser, and only when the