Module @swim/time

Swim Swim Time Library

The Swim Time library implements date-time, time zone, and time interval data types, with strptime/strftime-style parsers and formatters. The Swim Time library facilitates parsing and formatting of date strings, time zone aware date manipulation, and sampling of date ranges at regular time intervals.



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

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

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

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

The DateTime.fromLike 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.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""2019-08-12T16:35:10.838Z");
// "2019-08-12T16:36:00.000Z""2019-08-12T16:35:10.838Z", 30);
// "2019-08-12T17:05:00.000Z"

// "2019-08-12T16:00:00.000Z""2019-08-12T16:35:10.838Z");
// "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.

// "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"]




Type Aliases



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