datetime-attribute

Generate valid datetime attributes for the <time> HTML element.

Usage no npm install needed!

<script type="module">
  import datetimeAttribute from 'https://cdn.skypack.dev/datetime-attribute';
</script>

README

datetime-attribute

Get a valid datetime attribute for HTML <time> (among others).

The whole datetime specification is covered in 4 functions:

Additionally, a DateTime class and some other functions are provided.

The package is lightweight (~ 1.2 KB compressed for import *), tree-shakeable and include types.

Node.js CI

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 a NPM user? Download the package files in your project.

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`

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)

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 valut: true).

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

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

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

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

Changelog

See CHANGELOG.md or the releases.

Browser and tooling support

datetime-attribute is provided 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’d like one of those features, feel free to open an issue and/or a PR that won’t have any side effects for modern usage. Read more about ESModules.

Not only in <time>

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

License

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