2KB immutable date time library alternative to Moment.js with the same modern API

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Day.js Extended

Fast 2kB alternative to Moment.js with the same modern API

(This is an extended fork of the original project.)

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Day.js is a minimalist JavaScript library that parses, validates, manipulates, and displays dates and times for modern browsers with a largely Moment.js-compatible API. If you use Moment.js, you already know how to use Day.js.

dayjs().startOf('month').add(1, 'day').set('year', 2018).format('YYYY-MM-DD HH:mm:ss');

  • 🕒 Familiar Moment.js API & patterns
  • 💪 Immutable
  • 🔥 Chainable
  • 🌐 I18n support
  • 📦 2kb mini library
  • 👫 All browsers supported

Extensions to the original project

  • New plugin "customParseFormat" to parse input strings using custom formats.
  • New plugin "localizableFormat" to format dates according to the chosen locale.
  • New plugin "timeZone" to parse from and format to a date string using a time zone specified by its canonical name.
  • Corrected plugin "relativeTime" honouring grammar rules of the supported languages.
  • "UTC mode" for working in UTC, or for working with date-only values without the time part.
  • Additional locales (cs, ru, sk, uk).
  • Check for dayjs instance by the instanceof operator.


Day.js is usually imported via a "proxy module", which loads required plugins and registers required language packs. For example, via the following dayjs-local.js:
// Load dayjs, plugins and language packs.
import dayjs from 'dayjs-ext'
// import "timeZone-1900-2050", "timeZone-1970-2038"
// or "timeZone-2012-2022" to save your package size
import timeZonePlugin from 'dayjs-ext/plugin/timeZone'
import customParseFormat from 'dayjs-ext/plugin/customParseFormat'
import localizableFormat from 'dayjs-ext/plugin/localizableFormat'
import relativeTime from 'dayjs-ext/plugin/relativeTime'
import 'dayjs-ext/locale/cs'
import 'dayjs-ext/locale/sk'

// Register plugins and language packs; Czech will be the default language.

export default dayjs

Typical usage scenarios:
import dayjs from './dayjs-local'

// Load a date+time from a storage and show it to the user.
const dateTime = dayjs('2018-10-28T18:45:00.000Z')
console.log(dateTime.format({ format: 'L LT', timeZone: 'Europe/Prague' }))
// Prints "28.10.2018 19:45".
// Prints "před 5 hodinami" (5 hours ago).

// Read a date+time from the user and format it for the storage.
const dateTime = dayjs('28.10.2018 19:45', { format: 'L LT', timeZone: 'Europe/Prague' })
// Prints "2018-10-28T18:45:00.000Z".

// Set only the date; zero the time and prevent local time zone conversion.
const dateOnly = dayjs('2018-10-28', { utc: true })
console.log(dateOnly.format({ format: 'YYYY-MM-DD' }))
// Prints "2018-10-28" anytime and anywhere.

If used in the browser, the following scripts would be needed:
<-- include "index-1900-2050", "index-1970-2038"
    or "index-2012-2022" to save your package size -->
<script arc=""></script>
<script arc=""></script>
<script arc=""></script>
<script arc=""></script>
<script arc=""></script>
<script arc=""></script>
<script arc=""></script>

Getting Started


npm install dayjs-ext --save

📚Installation Guide


It's easy to use Day.js APIs to parse, validate, manipulate, and display dates and times.
dayjs('2018-08-08') // parse

dayjs().format('{YYYY} MM-DDTHH:mm:ss SSS [Z] A') // display

dayjs().set('month', 3).month() // get & set

dayjs().add(1, 'year') // manipulate

dayjs().isBefore(dayjs()) // query

📚API Reference


Day.js has great support for internationalization.
But none of them will be included in your build unless you use it.
import 'dayjs-ext/locale/es' // load on demand

dayjs.locale('es') // use Spanish locale globally

dayjs('2018-05-05').locale('zh-cn').format() // use Chinese Simplified locale in a specific instance


A plugin is an independent module that can be added to Day.js to extend functionality or add new features.
import timeZone from 'dayjs-ext/plugin/timeZone' // load on demand

dayjs.extend(timeZone) // use plugin

dayjs().format('D.M.YYYY H:mm',
  { timeZone: 'Europe/Berlin' }) // convert to CET before formatting

📚Plugin List


See the sponsor list at the original project. Thank you for your support!


See the contributor list at the original project. Thank you for your help!


Day.js is Extended licensed under a MIT License.