Date.getTime()
Returns the number of milliseconds since midnight Jan 1 1970, and a specified date
The getTime() method returns the numeric value corresponding to the time for the specified date according to universal time.
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.
var moonLanding = new Date('July 20, 69 00:20:18 GMT+00:00');
// milliseconds since Jan 1, 1970, 00:00:00.000 GMT
console.log(moonLanding.getTime());
// expected output: -14254782000
Syntax
dateObj.getTime()
Return value
A number representing the milliseconds elapsed between 1 January 1970 00:00:00 UTC and the given date.
Examples
Using getTime()
for copying dates
getTime()
for copying datesConstructing 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');
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 20us 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 enabled privacy.resistFingerprinting
, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds
, whichever is larger.
References
Contributors to this page
Uros Durdevic
Last updated