Date.now() - JavaScript 编辑

The static Date.now() method returns the number of milliseconds elapsed since January 1, 1970 00:00:00 UTC.

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Syntax

var timeInMs = Date.now();

Return value

A Number representing the milliseconds elapsed since the UNIX epoch.

Polyfill

This method was standardized in ECMA-262 5^th edition. Engines which have not been updated to support this method can work around the absence of this method using the following shim:

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

Examples

Reduced time precision

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 20µs in Firefox 59; in 60 it will be 2ms.

// reduced time precision (2ms) in Firefox 60
Date.now()
// 1519211809934
// 1519211810362
// 1519211811670
// ...

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

In Firefox, you can also enable privacy.resistFingerprinting, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds, whichever is larger.

Specifications

Browser compatibility

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The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Performance.now() — provides timestamps with sub-millisecond resolution for use in measuring web page performance
• console.time() / console.timeEnd()