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@thi.ng/date

date

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This project is part of the @thi.ng/umbrella monorepo.

About

Datetime types, relative dates, math, iterators, composable formatters, locales.

Status

STABLE - used in production

Search or submit any issues for this package

Installation

yarn add @thi.ng/date

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/date"></script>

Skypack documentation

For NodeJS (v14.6+):

node --experimental-specifier-resolution=node --experimental-repl-await

> const date = await import("@thi.ng/date");

Package sizes (gzipped, pre-treeshake): ESM: 5.59 KB

Dependencies

Usage examples

Several demos in this repo's /examples directory are using this package.

A selection:

ScreenshotDescriptionLive demoSource
Heatmap visualization of this mono-repo's commitsSource

API

Generated API docs

TODO - Please see tests and doc strings in source for now...

DateTime

The DateTime class acts as a thin wrapper around UTC epochs/timestamps, with the constructor supporting coercions and varying granularity/precision (from years to milliseconds). Default precision is milliseconds.

KeyPrecision
yYear
MMonth
dDay
hHour
mMinute
sSecond
tMillisecond

Note: DateTime instances also define the above keys as properties, plus getters for week-in-year (.w) and quarter (.q).

// create w/ current date (or pass epoch, string, Date or DateTime instances)
const a = dateTime();
// DateTime { y: 2020, M: 8, d: 19, h: 12, m: 17, s: 16, t: 884 }

// provide additional precision (here year only)
const b = dateTime(a, "y");
// or
const b = a.withPrecision("y")
// DateTime { y: 2020, M: 0, d: 1, h: 0, m: 0, s: 0, t: 0 }

a.toString();
// Sat Sep 19 2020 12:17:16 GMT'
a.toISOString()
// '2020-09-19T12:17:16.884Z'

b.toISOString();
// 2020-01-01T00:00:00.000Z

a.isLeapYear()
// true

a.daysInMonth()
// 30

a.dayInYear()
// 263

a.weekInYear()
// 38

a.isAfter(b)
// true\

b.isBefore(a)
// true

Math & comparison

DateTime instances support basic math to derive future/past instances, given an offset period. Period identifiers are any Precision ID (see above) or w (week, aka 7 days) or q (quarter, aka 3 months):

const a = dateTime();
// DateTime { y: 2020, M: 8, d: 19, h: 12, m: 17, s: 16, t: 884 }

// create new instance 61 seconds in the future
// any `Period` ID can be used
a.add(61, "s")
// DateTime { y: 2020, M: 8, d: 19, h: 12, m: 18, s: 17, t: 884 }

// ...or 90 days ago
a.add(-90, "d")
// DateTime { y: 2020, M: 5, d: 21, h: 12, m: 17, s: 16, t: 884 }

// ...or 2 quarters (aka 2x 3 months) ahead of time
a.add(2, "q").toISOString()
// "2021-03-19T12:17:16.884Z"

// check for equivalence
a.equiv("2020-09-19T12:17:16.884Z")
// true

// are dates equal (with tolerance of ±100 ms)
a.eqDelta(a.add(99, "t"), 100)
// true

a.compare(a.add(1, "s"))
// -1000

// compute difference between dates (in milliseconds)
difference(a, "1970-01-01") === a.getTime()
// true

difference("2021-02", "2020-02")
// 31622400000

difference("2021-02", "2020-02") / DAY
// 366 (because 2020 was a leap year)

Iterators

Several iterators are provided to produce timestamps of various granularities between two given dates. Originally, these were intended for visualization purposes (i.e. as axis tick label generators for @thi.ng/viz).

  • years()
  • querters()
  • months()
  • weeks()
  • days()
  • hours()
  • minutes()
  • seconds()
  • milliseconds()
[...months("2021-01-03", "2021-07-16")]
// [
// 1609459200000,
// 1612137600000,
// 1614556800000,
// 1617235200000,
// 1619827200000,
// 1622505600000,
// 1625097600000
// ]

[...months("2021-01-03", "2021-07-16")].map((x) => FMT_yyyyMMdd(x))
// [
// '2021-02-01',
// '2021-03-01',
// '2021-04-01',
// '2021-05-01',
// '2021-06-01',
// '2021-07-01'
// ]

Relative dates

Parsing

Relative dates can be obtained via parseRelative() or relative().

const now = dateTime();
// DateTime { y: 2021, M: 2, d: 21, h: 14, m: 26, s: 0, t: 661 }

// see the linked documentation for all supported formats
parseRelative("2 weeks ago", now);
// DateTime { y: 2021, M: 2, d: 7, h: 14, m: 26, s: 0, t: 661 }

parseRelative("an hour", now);
// DateTime { y: 2021, M: 2, d: 21, h: 15, m: 26, s: 0, t: 661 }

parseRelative("tomorrow", now);
// DateTime { y: 2021, M: 2, d: 22, h: 14, m: 26, s: 0, t: 661 }

parseRelative("-1 month", now)
// DateTime { y: 2021, M: 1, d: 21, h: 14, m: 26, s: 0, t: 661 }

Formatting

Dates can be formatted as relative descriptions using formatRelative() and formatRelativeParts(). Both functions use the currently active locale and accept an optional reference date (default: now).

setLocale(EN_LONG);

formatRelative("2020-06-01", "2021-07-01")
// "1 year ago"
formatRelative("2020-08-01", "2021-07-01")
// "11 months ago"
formatRelative("2021-07-01 13:45", "2021-07-01 12:05")
// "in 2 hours"
formatRelative("2021-07-01 12:23:24", "2021-07-01 12:05")
// "in 18 minutes"

// with default precision (seconds)
formatRelativeParts("2012-12-25 17:59:34", "2021-07-16 12:05")
// "8 years, 6 months, 21 days, 17 hours, 5 minutes, 26 seconds ago"

// with day precision
formatRelativeParts("2012-12-25 17:59:34", "2021-07-16 12:05", "d")
// "8 years, 6 months, 22 days ago"

// with month precision
formatRelativeParts("2012-12-25 17:59:34", "2021-07-16 12:05", "M")
// "8 years, 7 months ago"

formatRelativeParts("2021-07-16", "2021-01-01", "y")
// "in less than 1 year"

// with locale DE_LONG
withLocale(DE_LONG, () => formatRelativeParts("2020-01-01 12:34"))
// "vor 1 Jahr, 6 Monaten, 15 Tagen, 23 Stunden, 38 Minuten, 9 Sekunden"

// obtain the relative parts in raw form
// returns tuple of: [sign, years, months, days, hours, mins, secs, millis]
decomposeDifference("2020-01-01 12:34", Date.now())
// [-1, 1, 6, 15, 23, 38, 9, 703]

Date & time formatters

Custom date/time formatters can be assembled via defFormat(), using the following partial format identifiers. The MMM and E formatters use the currently active locale. To escape a formatter and use as a string literal, prefix the term with \\.

IDDescription
yyShort year (2 digits)
yyyyFull year (4 digits)
MUnpadded month
MMZero-padded 2-digit month
MMMMonth name in current locale (e.g. Feb)
dUnpadded day of month
ddZero-padded 2-digit day of month
EWeekday name in current locale (e.g. Mon)
wUnpadded week-in-year (ISO8601)
wwZero-padded 2-digit week-in-year (ISO8601)
qUnpadded quarter
HUnpadded hour of day (0-23)
HHZero-padded 2-digit hour of day (0-23)
hUnpadded hour of day (1-12)
mUnpadded minute of hour
mmZero-padded 2-digit minute of hour
sUnpadded second of minute
ssZero-padded 2-digit second of minute
SUnpadded millisecond of second
SSZero-padded 3-digit millisecond of second
A12-hour AM/PM marker (uppercase)
a12-hour am/pm marker (lowercase)
ZTimezone offset in signed ±HH:mm format
ZZSame as Z, but special handling for UTC
/EDLocale-specific weekday-day separator
/DMLocale-specific day-month separator
/MYLocale-specific month-year separator
/HMLocale-specific hour-minute separator

(Format IDs somewhat based on Java's SimpleDateFormat)

The following preset formatters are available:

  • FMT_ISO_SHORT - "2020-09-13T21:42:07Z"
  • FMT_yyyyMMdd - "2020-09-13"
  • FMT_Mdyyyy - "9/13/2020"
  • FMT_MMMdyyyy - "Sep 13 2020"
  • FMT_dMyyyy - "13/9/2020"
  • FMT_dMMMyyyy - "13 Sep 2020"
  • FMT_yyyyMMdd_HHmmss - 20200913-214207
  • FMT_HHmm - "21:42"
  • FMT_hm - "9:42 PM"
  • FMT_HHmmss - "21:42:07"
  • FMT_hms - "9:42:07 PM"

Timecodes

For timebased media applications, the higher-order defTimecode() can be used to create a formatter for a given FPS (frames / second, in [1..1000] range), e.g. HH:mm:ss:ff. The returned function takes a single arg (time in milliseconds) and returns formatted string.

The timecode considers days too, but only includes them in the result if the day part is non-zero. The 4 separators between each field can be customized via 2nd arg (default: all :).

a = defTimecode(30);
a(1*HOUR + 2*MINUTE + 3*SECOND + 4*1000/30)
// "01:02:03:04"

a(DAY);
// "01:00:00:00:00"

b = defTimecode(30, ["d ", "h ", "' ", '" ']);
b(Day + HOUR + 2*MINUTE + 3*SECOND + 999)
// "01d 01h 02' 03" 29"

Locales

The following locale presets are available by default:

PresetExample
DE_SHORT29.6.2021 @ 5:48
DE_LONGDienstag, 29. Juni 2021 @ 5:48
EN_SHORT29/06/2021 @ 5.48 am
EN_LONGTuesday 29 June 2021 @ 5.48 am
ES_LONGmartes 29 junio 2021 @ 5:48
FR_LONGmardi 29 juin 2021 @ 5h 48
IT_LONGmartedì 29 giugno 2021 @ 5.48

The MMM (month) and E (weekday) formatters make use of the strings provided by the current LOCALE (default: EN_SHORT) and can be set/changed via the setLocale() function:

const fmt = defFormat(["E", " ", "d", " ", "MMM", " ", "yyyy"]);

setLocale(EN_SHORT); // default
// {
// months: [
// 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
// 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'
// ],
// days: [ 'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat' ]
// }

fmt(dateTime());
// Sat 19 Sep 2020

setLocale(EN_LONG);

fmt(dateTime());
// Saturday 19 September 2020

Use withLocale() to only temporarily set a locale and execute a function with it, then automatically restoring the currently active locale.

fmt(dateTime());
// 'Fri 16 Jul 2021'

withLocale(FR_LONG, () => fmt(dateTime()));
// 'vendredi 16 juillet 2021'

fmt(dateTime());
// 'Fri 16 Jul 2021'

Authors

Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-date,
  title = "@thi.ng/date",
  author = "Karsten Schmidt",
  note = "https://thi.ng/date",
  year = 2020
}

License

© 2020 - 2021 Karsten Schmidt // Apache Software License 2.0

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