Event: timeStamp property

Value

The value is a DOMHighResTimeStamp representing the number of milliseconds elapsed from the relevant global object's time origin until the event was created. Its precision may be reduced to mitigate timing attacks and fingerprinting.

Example

HTML

<p>
  Focus this iframe and press any key to get the current timestamp for the
  keypress event.
</p>
<p>timeStamp: <span id="time">-</span></p>

JavaScript

function getTime(event) {
  const time = document.getElementById("time");
  time.firstChild.nodeValue = event.timeStamp;
}
document.body.addEventListener("keypress", getTime);

Result

Reduced time precision

To offer protection against timing attacks and fingerprinting, the precision of event.timeStamp may be reduced depending on browser settings.

Fractional milliseconds do not necessarily mean that time precision has not been reduced.

In Chrome, the rounding interval is 0.1 ms, or 0.005 ms in cross-origin-isolated contexts. In Safari, it is 1 ms, or 0.02 ms in cross-origin-isolated contexts.

In Firefox, the privacy.reduceTimerPrecision preference is enabled by default and uses a rounding interval of 1 ms, or 0.02 ms in cross-origin-isolated contexts. If privacy.resistFingerprinting is enabled, the rounding interval is 16.667 ms or the interval configured by privacy.resistFingerprinting.reduceTimerPrecision.microseconds, whichever is larger.

For example, these are possible values in Firefox:

// Reduced time precision (1 ms) in a non-isolated context
event.timeStamp;
// Might be:
// 9934
// 10363
// 11671
// …

// Reduced time precision with `privacy.resistFingerprinting` enabled
event.timeStamp;
// Might be:
// 10000.2
// 10016.867
// 10033.534
// …

Specifications

Browser compatibility