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Namespace @swim/time


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@swim/time provides date-time, time zone, and time interval data types, with strptime/strftime-style parsers and formatters. @swim/time facilitates parsing and formatting of date strings, time zone aware date manipulation, and sampling of date ranges at regular time intervals. @swim/time is part of the @swim/core framework.



The DateTime class models an immutable instant in time, relative to a particular TimeZone. The DateTime.current static method returns the current time in the local time zone, or in an optionally specified time zone.


The DateTime.from static method coerces plain JavaScript objects, of type DateTimeInit, to instances of DateTime. DateTime.from defaults to UTC, but can optionally be passed a specific time zone.

DateTime.from({year: 2019});
// "2019-01-01T00:00:00.000Z"

DateTime.from({year: 2019, month: 8, day: 12, hour: 5, minute: 16, second: 10});
// "2019-09-12T05:16:10.000Z"

DateTime.from({year: 2019, month: 8, day: 12, hour: 5, minute: 16, second: 10}, TimeZone.local());
// "2019-09-11T15:16:10.000Z"

The DateTime.fromAny static method coerces common JavaScript date representations, including ECMAScript Date objects, numbers representing milliseconds since the Unix epoch, and ISO 8601-formatted date-time strings, to DateTime instances.

// "2019-08-12T22:54:39.648Z"

// "2019-08-12T22:54:39.648Z"

// "2019-08-12T22:54:39.648Z"


The TimeZone class represents an immutable offset, in minutes, from Universal Coordinated Time (UTC). The TimeZone.local and TimeZone.utc static methods return the current local time zone, and the UTC time zone, respectively.

// TimeZone.forOffset(-420)

// TimeZone.forOffset(0)


A DateTimeFormat represents a string encoding that parse date-time strings as DateTime objects, and format DateTime objects as date-time strings. The DateTimeFormat.iso8601() static method returns the standard ISO 8601 date-time format. The DateTimeFormat.pattern method returns a DateTimeFormat that parses and formats date-times according to a strptime/strftime-style format string.

Use the parse method of a DateTimeFormat to parse a DateTime object from a compatible date-time string:

// "2019-08-12T16:11:59.586Z

// "2019-08-12T00:00:00.000Z"

// "1970-01-01T16:11:59.000Z"

Use the format method of a DateTimeFormat to serialize a DateTime object to a compatible date-time string. You can also optionally pass a DateTimeFormat to a DateTime's toString method.

// "2019-08-12T16:15:27.045Z"

// "2019-08-12"

// "16:16:20"

DateTime.current().toString(DateTimeFormat.pattern("%b %d"));
// "Aug 12"


A DateTimeLocale specifies the period, weekday, short weekday, month, and short month strings used when parsing and formatting date-time strings. DateTimeLocale.standard() returns the standard English language locale.


A TimeInterval represents a regular duration of time. A UnitTimeInterval represents a time interval with a uniform duration. Milliseconds, seconds, minutes, hours, and days are unit time intervals. Weeks, months, and years are not unit time intervals, because different weeks, months, and years can have different durations.

Time intervals can be created with the TimeInterval.millisecond, TimeInterval.second, TimeInterval.minute, TimeInterval.hour, TimeInterval.day, TimeInterval.week, TimeInterval.month, and TimeInterval.year factory methods.

A TimeInterval can be used to offset a DateTime by a multiple of the interval, to advance to the next whole multiple of the interval, to round a DateTime down to the floor of the interval, to round a DateTime up to the ceil of the interval, or to round a DateTime to the nearest whole interval.

TimeInterval.second().offset("2019-08-12T16:35:10.838Z", 5);
// "2019-08-12T16:35:15.838Z"

// "2019-08-12T16:36:00.000Z"

TimeInterval.minute().next("2019-08-12T16:35:10.838Z", 30);
// "2019-08-12T17:05:00.000Z"

// "2019-08-12T16:00:00.000Z"

// "2019-08-13T00:00:00.000Z"

// "2019-08-11T00:00:00.000Z"

The every method of a UnitTimeInterval returns a new TimeInterval equal to a multiple of the base time interval. The TimeInterval.millisecond, TimeInterval.second, TimeInterval.minute, TimeInterval.hour, TimeInterval.day factory methods also take an integer multiple as an optional argument, returning the equivalent of calling every on the base interval.

// "2019-08-12T16:45:00.000Z"

// "2019-08-12T16:45:00.000Z"

The range method of a TimeInterval returns an array of DateTimes representing every whole interval between some start time (inclusive), and some end time (exclusive). An optional third argument to range indicates that only every step multiple of the base interval should be included in the returned range.

The TimeInterval.milliseconds, TimeInterval.seconds, TimeInterval.minutes, TimeInterval.hours, TimeInterval.days, TimeInterval.weeks, TimeInterval.months, and TimeInterval.years factory methods provide a shorthand for computing a range of DateTimes between two times, and return the equivalent of calling range on the underlying time interval.

TimeInterval.year().range({year: 2017}, {year: 2020});
// ["2017-01-01T00:00:00.000Z", "2018-01-01T00:00:00.000Z", "2019-01-01T00:00:00.000Z"]

TimeInterval.months({year: 2019, month: 3}, {year: 2019, month: 6});
// ["2019-04-01T00:00:00.000Z", "2019-05-01T00:00:00.000Z", "2019-06-01T00:00:00.000Z"]

TimeInterval.days({year: 2019, month: 7, day: 1}, {year: 2019, month: 7, day: 12}, 4);
// ["2019-08-01T00:00:00.000Z", "2019-08-05T00:00:00.000Z", "2019-08-09T00:00:00.000Z"]



For an npm-managed project, npm install @swim/time to make it a dependency. TypeScript sources will be installed into node_modules/@swim/time/main. Transpiled JavaScript and TypeScript definition files install into node_modules/@swim/time/lib/main. And a pre-built UMD script can be found in node_modules/@swim/time/dist/main/swim-time.js.


Browser applications can load swim-core.js, which comes bundled with the @swim/time library, directly from the SwimOS CDN.

<!-- Development -->
<script src="https://cdn.swimos.org/js/latest/swim-core.js"></script>

<!-- Production -->
<script src="https://cdn.swimos.org/js/latest/swim-core.min.js"></script>

Alternatively, the standalone swim-system.js script may be loaded from the SwimOS CDN, which bundles @swim/time together with all other @swim/system libraries.

<!-- Development -->
<script src="https://cdn.swimos.org/js/latest/swim-system.js"></script>

<!-- Production -->
<script src="https://cdn.swimos.org/js/latest/swim-system.min.js"></script>



@swim/time can be imported as an ES6 module from TypeScript and other ES6-compatible environments.

import * as time from "@swim/time";


@swim/time can also be used as a CommonJS module in Node.js applications.

var time = require("@swim/time");


When loaded by a web browser, the swim-core.js script adds all @swim/time library exports to the global swim namespace.

The swim-system.js script also adds all @swim/time library exports to the global swim namespace, making it a drop-in replacement for swim-core.js when additional @swim/system libraries are needed.


Type aliases


AnyDateTime: DateTime | DateTimeInit | Date | string | number


AnyTimeZone: TimeZone | string | number

Object literals

Const DateTimeSpecifiers

DateTimeSpecifiers: object