Date.now()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Date.now() static method returns the number of milliseconds elapsed since the epoch, which is defined as the midnight at the beginning of January 1, 1970, UTC.

Try it

// This example takes 2 seconds to run
const start = Date.now();

console.log("starting timer...");
// Expected output: "starting timer..."

setTimeout(() => {
  const ms = Date.now() - start;

  console.log(`seconds elapsed = ${Math.floor(ms / 1000)}`);
  // Expected output: "seconds elapsed = 2"
}, 2000);

Syntax

Date.now()

Return value

A number representing the timestamp, in milliseconds, of the current time.

To offer protection against timing attacks and fingerprinting, the precision of Date.now() 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.

For example, with reduced time precision, the result of Date.now() will always be a multiple of 2, or a multiple of 100 (or privacy.resistFingerprinting.reduceTimerPrecision.microseconds) with privacy.resistFingerprinting enabled.

js
// reduced time precision (2ms) in Firefox 60
Date.now();
// Might be:
// 1519211809934
// 1519211810362
// 1519211811670
// …

// reduced time precision with `privacy.resistFingerprinting` enabled
Date.now();
// Might be:
// 1519129853500
// 1519129858900
// 1519129864400
// …

Examples

Measuring time elapsed

You can use Date.now() to get the current time in milliseconds, then subtract a previous time to find out how much time elapsed between the two calls.

js
const start = Date.now();
doSomeLongRunningProcess();
console.log(`Time elapsed: ${Date.now() - start} ms`);

For more complex scenarios, you may want to use the performance API instead.

Specifications

Specification

ECMAScript® 2027 Language Specification
# sec-date.now

Browser compatibility

Enable JavaScript to view this browser compatibility table.

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Standard built-in objects
Date
Constructor
1. Date()
Static methods
1. now()
2. parse()
3. UTC()
Instance methods
Inheritance
Object/Function
Static methods
Static properties
Instance methods
Instance properties
1. __proto__
2. constructor

Date.now()

In this article

Try it

Syntax

Parameters

Return value

Description

Reduced time precision

Examples

Measuring time elapsed

Specifications

Browser compatibility

See also

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