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meduzen/datetime-attribute

datetime-attribute

Get a datetime attribute for HTML <time> (and other elements).

It covers the whole WHATWG specification in 4 functions:

Additionally, a DateTime class (721 B) and some other functions are provided.

Node.js CI

The package is lightweight (~ 1.42 KB compressed for import *), tree-shakeable, typed and tested.

Table of contents

Summary usage

import * from 'datetime-attribute'

const now = new Date()

datetime(now)                   // '2021-03-14'
datetime(now, 'time')           // '10:29'
datetimeTz(now, 'datetime', -7) // '2021-03-14T10:29-07:00'
utc(now, 'time')                // '09:29Z'

tzOffset(-9, 30) // '-09:30' (Marquesas Islands)
duration({ d: 4, h: 3, m: 17 }) // 'P4DT3H17M'

const importantMeeting = new DateTime(2021, 12, 17, 19, 00) // 17/11
const meetingWeek = importantMeeting.getWeek() // 46

importantMeeting.setWeek(meetingWeek + 1) // meeting now on 24/11
importantMeeting.to('week')        // 2021W47
importantMeeting.to('datetime')    // 2021-11-24T19:00

daysBetween(now, importantMeeting) // 248

Installation

Install the package:

npm install datetime-attribute

Then, import the functions you need in your script:

// if you only need `datetime` and `duration`
import { datetime, duration } from 'datetime-attribute'

// if you need everything
import * from 'datetime-attribute'

Not using a package manager? Download the package files in your project and take the files in /src.

Expressing moments with datetime()

datetime() accepts two optional arguments: a Date object, and a precision keywords.

import { datetime } from 'datetime-attribute'

const now = new Date() // We’re 14 March 2021 and it’s 10:29 in Brussels.

datetime(now)             // '2021-03-14'
datetime(now, 'datetime') // '2021-03-14T10:29'

Without argument, it defaults to today:

datetime() // today formatted in YYYY-mm-dd
datetime((new Date()), 'day') // same

Available precision keywords

By default, datetime() precision is day, resulting in a YYYY-mm-dd output. Many other values are available.

Date

precision example output description
day 2021-03-14 the default, fitting a calendar
year 2021 only the year
yearless 03-14 a day in a month
month 2021-03 a month in a year
week 2021W10 the week number (ISO-8601 spec) and its year

Time and UTC time

Time:

precision example output description
time 10:29 hours and minutes, like most clocks
second 10:29:00 time with precision up to seconds
ms 10:29:00.000 time with precision up to milliseconds

To get UTC time, add utc to the time keyword:

precision example output description
time utc 09:29Z time, shifted to UTC time
second utc 09:29:00Z second, shifted to UTC time
ms utc 09:29:00.000Z ms, shifted to UTC time

Datetime and UTC datetime

Datetime:

precision example output description
datetime 2021-03-14T10:29 a local datetime (= date + time separated by T)
datetime second 2021-03-14T10:29:00 time with precision up to seconds
datetime ms 2021-03-14T10:29:00.000 time with precision up to milliseconds

To get UTC datetime, add utc to the datetime keyword:

precision example output description
datetime utc 2021-03-14T09:29Z datetime, shifted to UTC time
datetime second utc 2021-03-14T09:29:00Z datetime second, shifted to UTC time
datetime ms utc 2021-03-14T09:29:00.000Z datetime ms, shifted to UTC time

The utc shortcut

💡 Instead of adding utc to a time or datetime keyword, you can use utc(date, precision), which has datetime as default precision:

import { datetime, utc } from 'datetime-attribute'

const now =  new  Date()  // We’re 14 March 2021 and it’s 10:29 in Brussels.

// These are the same:
utc(now, 'time') // `09:29Z`
datetime(now, 'time utc') // `09:29Z`

// These are the same:
utc(now)             // `2021-03-14T09:29Z`
utc(now, 'datetime') // `2021-03-14T09:29Z`
datetime(now, 'datetime utc') // `2021-03-14T09:29Z`

Datetime separator

Per spec, the separator between date and time can be T (default) or (1 space).

To change the separator, use setTimeSeparator:

import { setTimeSeparator } from 'datetime-attribute'

setTimeSeparator(' ')

// All next datetime functions will follow the new setting.
datetime(now) // `2021-03-14 10:29`

// Switch back to the default.
setTimeSeparator('T') // or `setTimeSeparator()`

Setting the separator to a space can be useful to deal with MySQL or MariaDB DATETIME column.

Expressing timezone offsets with tzOffset()

Timezone offsets are a comparison against UTC time. For example, +01:00 means “one hour ahead of UTC time” and -05:00 means “five hours behind UTC time”.

tzOffset() accepts three optional arguments for hours, minutes, and compliance to real-life boundaries. Without argument, the local timezone offset is returned (and may differ based on daylight saving time).

import { tzOffset } from 'datetime-attribute'

tzOffset(3)      // '+03:00' (Moscow)

tzOffset(-9, 30) // '-09:30' (Marquesas Islands)
tzOffset(-9.5)   // '-09:30' (same with 1 parameter)

tzOffset(0)      //      'Z' (Ghana; 'Z' is equal to '+00:00')

// in Belgium
tzOffset()       // '+01:00'
tzOffset()       // '+02:00' (under daylight time saving)

Hours-minutes separator

Per spec, the separator between hours and minutes is optional. The allowed values are:

  • (default) a colon caracter (:);
  • an empty string.

To change the separator, use setTzSeparator:

import { setTzSeparator } from 'datetime-attribute'

setTzSeparator('')

// All next timezone-related functions will follow the new setting.
tzOffset(3)       // '+0300'
tzOffset(-9, 30)  // '-0930'

// Switch back to the default.
setTzSeparator(':')

Real-life timezone offset

The timezone offset will be adjusted to fit in the spec range (from -23:59 to +23:59). This means tzOffset(44) will output +20:00 instead of +44:00.

However, timezone offsets of countries in the world are all between -12:00 and +14:00. If you want tzOffset(44) to output -04:00 so that it matches real-life boundaries, give it a third parameter (default: false):

tzOffset(44) // '+20:00'
tzOffset(44, 0, true) // '-04:00'

Curious about timezones? Have a look at the timezone map and the daylight time saving chaos.

Adding a timezone offset to a moment with datetimeTz()

As datetime() doesn’t care about timezones, you can use datetimeTz() when you need to be explicit about the timezone of a moment.

💡 datetimeTz() is basically a concatenation of datetime(date, precision) and tzOffset(hours, minutes), so be sure to read about them.

It accepts the same 5 parameters, all optional:

datetimeTz(date, precision, offsetHours, offsetMinutes, inRealLifeBoundaries)
  1. A date object (default: new Date())
  2. A precision keywords among:
    • time
    • second
    • ms
    • datetime (default)
    • datetime second
    • datetime ms
  3. Hours offset like in tzOffset()
  4. Minutes offset like in tzOffset()
  5. Boundaries of the timezone offset like in tzOffset()

When hours and minutes are not specified, the local timezone offset is used.

import { datetime, datetimeTz } from 'datetime-attribute'

const now = new Date() // We’re 2 April 2021 and it’s 23:51 in Brussels.

datetime(now)   // '2021-04-02'
datetimeTz(now) // '2021-04-02T23:51+02:00'

datetime(now, 'time')           // '23:51'
datetime(now, 'time utc')       // '21:51Z' (same as previous, converted to UTC)
datetimeTz(now, 'time', 0)      // '23:51Z' (datetimeTz does not convert)
datetimeTz(now, 'time')         // '23:51+02:00' (fall back on local timezone)
datetimeTz(now, 'time', 9)      // '23:51+09:00'
datetimeTz(now, 'time', -3, 30) // '23:51-03:30'
datetimeTz(now, 'time', -14, 0, true) // '23:51+10:00'

datetimeTz() does not convert your moment to another timezone: it only adds the wanted timezone to the moment. Its purpose is to generate a valid datetime attribute saying “here’s a moment, it has this [hours, minutes] timezone offset”.

Let’s take this sentence and its HTML:

When I’m in Brussels, I wake up at 8 o’clock every day.

<p>When I’m in Brussels, I wake up <time datetime="08:00+02:00">at 8 o’clock</time> every day.</p>

Here’s how you can get the datetime attribute fitting this sentence:

// const awakeningAt = new Date(…) // a Date object with 08:00 as time

datetimeTz(awakeningAt, 'time', 2) // '08:00+02:00'

Expressing durations with duration()

duration() requires an object with entries for different levels of durations, from seconds to weeks. It also accepts a second parameter to control the conversion of units overflow (default: true).

import { duration } from 'datetime-attribute'

const countdownBeforeBigParty = {
  w: 3,   //     3 weeks
  d: 5,   //     5 days
  h: 10,  //    10 hours
  m: 43,  //    43 minutes
  s: 2.61 // 2.610 seconds
}

duration(countdownBeforeBigParty) // 'P3W5DT10H43M2'

All object keys are optional:

duration({ h: 17 }) // 'PT17H'

Units overflow

Values exceeding a unit are converted to upper units:

duration({ h: 31, m: 63, s: 175 }) // 'P1DT8H5M55S'

If you don’t need this behaviour, pass false as second parameter (default value: true).

duration({ m: 175 }) // 'PT2H55M'
duration({ m: 175 }, false) // 'PT175M'

The DateTime class

The DateTime class extends the native Date object with methods allowing you to interact with the week number or to output a datetime string.

Constructor

Its constructor remains the same as the Date one.

import { DateTime } from 'datetime-attribute'

// One of the many ways to instantiate a `Date`, and this `DateTime`.
const summer = new DateTime(2021, 5, 21) // June 21, 2021

DateTime.prototype.getWeek()

Returns the week of the year, giving the same output as weekNumber().

const summer = new DateTime(2021, 5, 21) // June 21, 2021

summer.getWeek() // 25

DateTime.prototype.setWeek()

Shifts the date to the provided week, while preserving its initial day. In other words, if the initial date is a Friday, then the shifted date remains a Friday.

const summer = new DateTime(2021, 5, 21) // June 21, 2021

summer.setWeek(26) // shifts the date to June 28, 2021
summer.getWeek() // now it’s 26

DateTime.prototype.to()

Returns a datetime attribute. DateTime.to() accepts the same precision keywords as datetime().

const summer = new DateTime(2021, 5, 21) // June 21, 2021

summer.to('month') // 2021-06
summer.to('yearless') // 06-21
summer.to('datetime second') // 2021-06-21T00:00:00

Other functions

Under the hood, the core features of datetime-attribute uses additional functions that you can also import individually.

daysBetween()

Calculate the difference between 2 dates in days, discarding the time of day. It subtracts the first Date object from the second one.

import { daysBetween } from 'datetime-attribute'

const january1st = new Date(2021, 0, 1, 10, 10, 12)
const january11th = new Date(2021, 0, 11, 10, 10, 12)
const january19th = new Date(2021, 0, 19, 10, 10, 12)

daysBetween(january1st, january11th) // 10
daysBetween(january19th, january11th) // -8

(134 B)

weekNumber()

Get the week number as defined by the WHATWG, following the ISO-8601 specs:

It accepts a Date object.

import { weekNumber } from 'datetime-attribute'

const january1st = new Date(2021, 0, 1, 10, 10, 12)
const january11th = new Date(2021, 0, 11, 10, 10, 12)
const togoIndependanceDay = new Date(1960, 3, 27)

weekNumber(togoIndependanceDay) // 17
weekNumber(january1st) // 53: it’s a Friday!
weekNumber(january11th) // 2

(201 B)

Changelog

See CHANGELOG.md or the releases.

Browser and tooling support

datetime-attribute is provided as module for modern browsers usage with standard JavaScript syntax:

  • it is up to you to transpile it for legacy browsers;
  • you can’t import it using require('datetime-attribute');
  • if you don’t transpile it, DateTime requires support for class fields (Safari 14.0) starting v1.32.0.

Read more about ESModules.

Not only in <time>

<time> is not alone! Other elements can benefit from datetime-attribute:

Security

See the security policy.

Contributing

See the contributing guidelines.

License

The datetime-attribute package is open-sourced software licensed under the DWTFYWTPL.