Fix first visible timestamp and LCPV #37144
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In ampproject#36273, I switched from `Date.now()` to `performance.now()`, thinking it was a higher resolution timestamp time since the unix epoch. But, `peformance.now` is relative to _page load time_ (or `timeOrigin`), not the epoch. This matters because our "since visible" metrics use the epoch as their base time, meaning the timestamps are roughly 1.6 trillion milliseconds. But `performance.now` is tiny, in the range of a few million for a page that was loaded an hour ago. When we calculated the "since visible", we received values that were still in the trillions when we expect millions. By adding `performance.now()` and `performance.timeOrigin`, we get a timestamp relative to the epoch. Now when we calculate the "since visible", we get the correct values.
samouri
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Dec 7, 2021
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In #36273, I switched from `Date.now()` to `performance.now()`, thinking it was a higher resolution timestamp time since the unix epoch. But, `performance.now` is relative to _page load time_ (or `performance.timeOrigin`), not the epoch. This matters because our "since visible" metrics use the epoch as their base time, meaning the timestamps are roughly 1.6 trillion milliseconds. But `performance.now` is tiny, in the range of a few million for a page that was loaded an hour ago. When we calculated the "since visible", we received values that were still in the trillions when we expect millions. By adding `performance.now()` and `performance.timeOrigin`, we get a timestamp relative to the epoch. Now when we calculate the "since visible", we get the correct values. (cherry picked from commit 7645c4e)
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In #36273, I switched from
Date.now()toperformance.now(), thinking it was a higher resolution timestamp time since the unix epoch. But,performance.nowis relative to page load time (orperformance.timeOrigin), not the epoch.This matters because our "since visible" metrics use the epoch as their base time, meaning the timestamps are roughly 1.6 trillion milliseconds. But
performance.nowis tiny, in the range of a few million for a page that was loaded an hour ago. When we calculated the "since visible", we received values that were still in the trillions when we expect millions.By adding
performance.now()andperformance.timeOrigin, we get a timestamp relative to the epoch. Now when we calculate the "since visible", we get the correct values.Fixes #37072.