Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
read-only property returns an
unsigned long long representing the moment,
in milliseconds since the UNIX epoch, right after the prompt for unload terminates on
the previous document in the same browsing context. If there is no previous document,
this value will be the same as
unsigned long long.
BCD tables only load in the browser
PerformanceTiminginterface it belongs to.