Date.prototype.getTime()

A number representing the timestamp, in milliseconds, of this date. Returns NaN if the date is invalid.

Date objects are fundamentally represented by a timestamp, and this method allows you to retrieve the timestamp. 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.

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 2ms. You can also enable privacy.resistFingerprinting, in which case the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds, whichever is larger.

// 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
// …

Constructing a date object with the identical time value.

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

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.

let end, start;

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

console.log(`Operation took ${end.getTime() - start.getTime()} msec`);

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