Date.prototype.getTime()

The getTime() method returns the number of milliseconds* since the Unix Epoch.

* JavaScript uses milliseconds as the unit of measurement, whereas Unix Time is in seconds.

getTime() always uses UTC for time representation. For example, a client browser in one timezone, getTime() will be the same as a client browser in any other timezone.

You can use this method to help assign a date and time to another Date object. This method is functionally equivalent to the valueOf() method.

Syntax

getTime()

Return value

A number representing the milliseconds elapsed between 1 January 1970 00:00:00 UTC and the given date.

Reduced time precision

To offer protection against timing attacks and fingerprinting, the precision of new Date().getTime() might get rounded depending on browser settings. In Firefox, the privacy.reduceTimerPrecision preference is enabled by default and defaults to 20µs in Firefox 59; in 60 it will be 2ms.

// reduced time precision (2ms) in Firefox 60
new Date().getTime();
// 1519211809934
// 1519211810362
// 1519211811670
// ...

// reduced time precision with `privacy.resistFingerprinting` enabled
new Date().getTime();
// 1519129853500
// 1519129858900
// 1519129864400
// ...

In Firefox, you can also enable privacy.resistFingerprinting, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds, whichever is larger.

Examples

Using getTime() for copying dates

Constructing a date object with the identical time value.

// Since month is zero based, birthday will be January 10, 1995
var birthday = new Date(1994, 12, 10);
var copy = new Date();
copy.setTime(birthday.getTime());

Measuring execution time

Subtracting two subsequent getTime() calls on newly generated Date objects, give the time span between these two calls. This can be used to calculate the executing time of some operations. See also Date.now() to prevent instantiating unnecessary Date objects.

var end, start;

start = new Date();
for (var i = 0; i < 1000; i++) {
  Math.sqrt(i);
}
end = new Date();

console.log('Operation took ' + (end.getTime() - start.getTime()) + ' msec');

Specifications

Browser compatibility

See also

• Date.prototype.setTime()
• Date.prototype.valueOf()
• Date.now()