High-resolution timestamps

performance.now() returns a precise timestamp: The number of milliseconds, including microseconds, since the current web page started to load.

More generally, it returns the time elapsed since the performanceTiming.navigationStart event.

t = performance.now();

For example, in a web browser’s main context, performance.now() returns 6288.319 if the web page began to load 6288 milliseconds and 319 microseconds ago.