Performance.now

The performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds, accurate to five thousandths of a millisecond (5 microseconds).

The returned value represents the time elapsed since the time origin.

Bear in mind the following points:

• In dedicated workers created from a Window context, the value in the worker will be lower than performance.now() in the window who spawned that worker. It used to be the same as t0 of the main context, but this was changed.
• In shared or service workers, the value in the worker might be higher than that of the main context because that window can be created after those workers.

Syntax

t = performance.now();

Example

var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.");

Unlike other timing data available to JavaScript (for example Date.now), the timestamps returned by Performance.now() are not limited to one-millisecond resolution. Instead, they represent times as floating-point numbers with up to microsecond precision.

Also unlike Date.now(), the values returned by Performance.now() always increase at a constant rate, independent of the system clock (which might be adjusted manually or skewed by software like NTP). Otherwise, performance.timing.navigationStart + performance.now() will be approximately equal to Date.now().

Specifications

Browser compatibility

[1] Windows versions of Chrome 20 through 33 return performance.now() only to millisecond precision.

[2] Starting with Firefox 57.0.4, the accuracy of this function has been reduced to 20 microseconds on the desktop and Android platforms, while the Mozilla team investigate a security issue related to the precise timing of events. The accuracy may be increased at a later date.

See also

• When milliseconds are not enough: performance.now() from HTML5 Rocks.