.unloadEventStart read-only property returns an
unsigned long long representing the moment, in miliseconds 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.
PerformanceTiminginterface it belongs to.