What Time is it?
Sometimes measuring time in millisecond resolution just isn’t accurate enough. Together with industry and community leaders, the W3C Web Performance working group has worked to solve this problem by standardizing the High Resolution Time specification.
To solve this issue, the High Resolution Time specification defines a new time base with at least microsecond resolution (one thousandth of a millisecond). To reduce the number of bits used to represent this number and to increase readability, instead of measuring time from 01 January, 1970 UTC, this new time base measures time from the beginning of navigation of the document, performance.timing.navigationStart. This time base is also different in that it is monotonically increasing and not subject to clock skew or adjustment. The difference between subsequent calls to performance.now() will never be negative.
The specification defines
performance.now() as the analogous method to
Date.now() for determining the current time in high
DOMHighResTimeStamp is the analogous type to
DOMTimeStamp that defines the high resolution time value.