# Timestamps

# High-resolution timestamps

performance.now() (opens new window) returns a precise timestamp: The number of milliseconds, including microseconds, since the current web page started to load.

More generally, it returns the time elapsed since the performanceTiming.navigationStart (opens new window) event.

t = performance.now();

For example, in a web browser's main context, performance.now() returns 6288.319 if the web page began to load 6288 milliseconds and 319 microseconds ago.

# Low-resolution timestamps

Date.now() (opens new window) returns the number of whole milliseconds that have elapsed since 1 January 1970 00:00:00 UTC.

t = Date.now();

For example, Date.now() returns 1461069314 if it was called on 19 April 2016 at 12:35:14 GMT.

# Get Timestamp in Seconds

To get the timestamp in seconds

Math.floor((new Date().getTime()) / 1000)

# Support for legacy browsers

In older browsers where Date.now() is unavailable, use (new Date()).getTime() (opens new window) instead:

t = (new Date()).getTime();

Or, to provide a Date.now() function for use in older browsers, use this polyfill (opens new window):

if (!Date.now) {
  Date.now = function now() {
    return new Date().getTime();
  };
}

# Syntax

millisecondsAndMicrosecondsSincePageLoad = performance.now();
millisecondsSinceYear1970 = Date.now();
millisecondsSinceYear1970 = (new Date()).getTime();

# Remarks

performance.now() is available in modern web browsers (opens new window) and provides reliable timestamps with sub-millisecond resolution.

Since Date.now() and (new Date()).getTime() are based on the system time, they often get skewed by a few milliseconds when the system time is automatically synchronized (opens new window).

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