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README.md

@thi.ng/date

npm version npm downloads Mastodon Follow

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 Node.js REPL:

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

Package sizes (brotli'd, pre-treeshake): ESM: 5.13 KB

Dependencies

Usage examples

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

A selection:

Screenshot Description Live demo Source
Heatmap visualization of this mono-repo's commits Source
Zig-based To-Do list, DOM creation, local storage task persistence Demo Source

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.

Key Precision
y Year
M Month
d Day
h Hour
m Minute
s Second
t Millisecond

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]

// format a duration (in ms), optionally with given precision
formatDuration(45296000)
// "12 h, 34 min, 56 s"

formatDuration(45296000, "h")
// "13 h"

formatDuration(45296000,"d")
// "< 1 d"

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 \\.

ID Description
yy Short year (2 digits)
yyyy Full year (4 digits)
M Unpadded month
MM Zero-padded 2-digit month
MMM Month name in current locale (e.g. Feb)
d Unpadded day of month
dd Zero-padded 2-digit day of month
E Weekday name in current locale (e.g. Mon)
w Unpadded week-in-year (ISO8601)
ww Zero-padded 2-digit week-in-year (ISO8601)
q Unpadded quarter
H Unpadded hour of day (0-23)
HH Zero-padded 2-digit hour of day (0-23)
h Unpadded hour of day (1-12)
m Unpadded minute of hour
mm Zero-padded 2-digit minute of hour
s Unpadded second of minute
ss Zero-padded 2-digit second of minute
S Unpadded millisecond of second
SS Zero-padded 3-digit millisecond of second
A 12-hour AM/PM marker (uppercase)
a 12-hour am/pm marker (lowercase)
Z Timezone offset in signed ±HH:mm format
ZZ Same as Z, but special handling for UTC
/ED Locale-specific weekday-day separator
/DM Locale-specific day-month separator
/MY Locale-specific month-year separator
/HM Locale-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:

Preset Example
DE_SHORT 29.6.2021 @ 5:48
DE_LONG Dienstag, 29. Juni 2021 @ 5:48
EN_SHORT 29/06/2021 @ 5.48 am
EN_LONG Tuesday 29 June 2021 @ 5.48 am
ES_LONG martes 29 junio 2021 @ 5:48
FR_LONG mardi 29 juin 2021 @ 5h 48
IT_LONG martedì 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

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 - 2023 Karsten Schmidt // Apache License 2.0