read-only property returns an
unsigned long long representing the moment,
in milliseconds since the UNIX epoch, the
unload event has been thrown. If
there is no previous document, or if the previous document, or one of the needed
redirects, is not of the same origin, the value returned is
time = performanceTiming.unloadEventStart;
The definition of 'PerformanceTiming.unloadEventStart' in that specification.
BCD tables only load in the browser
PerformanceTiminginterface it belongs to.