The loadEventStart property must return the time immediately before the load event of the current document is fired. It must return zero if the load event has not been fired.
An Integer value that represents the time immediately before the load event of the current document is fired. It must return zero if the load event has not been fired.
- Navigation Timing, Section 4.2
The value reported by the loadEventStart property represents the number of milliseconds between the recorded time and midnight January 1, 1970 (UTC).
The following example shows how to calculate the amount of time required to execute the onload event for the document.
var oTiming = window.performance.timing; var iTimeMS = oTiming.loadEventEnd - oTiming.loadEventStart;