How Do I Get a Timestamp in JavaScript?

Obtaining a Timestamp in JavaScript

The need for a single numerical representation of the current date and time, such as a Unix timestamp, often arises in programming tasks. JavaScript offers multiple ways to retrieve timestamps:

Timestamp in Milliseconds:

The number of milliseconds elapsed since the Unix epoch (January 1, 1970, 00:00:00 UTC) can be obtained using:

• Date.now(): Call this function to retrieve the current timestamp.
• new Date(): Use the unary operator to cast Date.prototype.valueOf to a number.
• new Date().valueOf(): Directly call valueOf on a new Date object.

For compatibility with Internet Explorer 8 and earlier, consider creating a shim for Date.now:

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

You can also call getTime directly: new Date().getTime().

Timestamp in Seconds:

To obtain the number of seconds since the Unix epoch (i.e., a Unix timestamp):

Math.floor(Date.now() / 1000)

A slightly faster alternative that may be less readable and potentially break in the future:

Date.now() / 1000 | 0

Timestamp in Milliseconds (Higher Resolution):

Leverage the performance API, specifically performance.now, to achieve a higher-resolution timestamp:

var isPerformanceSupported = (
  window.performance &&
  window.performance.now &&
  window.performance.timing &&
  window.performance.timing.navigationStart
);

var timeStampInMs = (
  isPerformanceSupported ?
  window.performance.now() +
  window.performance.timing.navigationStart :
  Date.now()
);

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