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Intl.DateTimeFormat (ESNext)

A spec-compliant polyfill for Intl.DateTimeFormat fully tested by the official ECMAScript Conformance test suite

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Right now we only support Gregorian calendar in this polyfill. Therefore we recommend setting calendar: 'gregory' in your options to be safe.


Right now this polyfill supports daylight transition until 2100 to reduce the dataset size



npm i @formatjs/intl-datetimeformat


This package requires the following capabilities:



You can use URL Builder to create a polyfill script tag for Intl.DateTimeFormat. By default the created URL does not come with any locale data. In order to add locale data, append Intl.DateTimeFormat.~locale.<locale>, as well as locale data for any required polyfills, to your list of features. For example:

<!-- Polyfill Intl.DateTimeFormat, its dependencies & `en` locale data -->
<script src=",Intl.DateTimeFormat.~locale.en,Intl.NumberFormat.~locale.en"></script>


import '@formatjs/intl-datetimeformat/polyfill'
import '@formatjs/intl-datetimeformat/locale-data/en' // locale-data for en
import '@formatjs/intl-datetimeformat/add-all-tz' // Add ALL tz data

Dynamic import + capability detection

import {shouldPolyfill} from '@formatjs/intl-datetimeformat/should-polyfill'
async function polyfill(locale: string) {
const unsupportedLocale = shouldPolyfill(locale)
// This locale is supported
if (!unsupportedLocale) {
// Load the polyfill 1st BEFORE loading data
await import('@formatjs/intl-datetimeformat/polyfill-force')

// Parallelize CLDR data loading
const dataPolyfills = [
await Promise.all(dataPolyfills)

Adding IANA Timezone Database

We provide 2 pre-processed IANA Timezone:

Full: contains ALL Timezone from IANA database

import '@formatjs/intl-datetimeformat/polyfill'
import '@formatjs/intl-datetimeformat/add-all-tz'
import '@formatjs/intl-datetimeformat/polyfill'
import '@formatjs/intl-datetimeformat/add-golden-tz'

Default Timezone

Since JS Engines do not expose default timezone, there's currently no way for us to detect local timezone that a browser is in. Therefore, the default timezone in this polyfill is UTC.

You can change this by either calling __setDefaultTimeZone or always explicitly pass in timeZone option for accurate date time calculation.

Since __setDefaultTimeZone is not in the spec, you should make sure to check for its existence before calling it & after tz data has been loaded, e.g:

import '@formatjs/intl-datetimeformat/polyfill'
import '@formatjs/intl-datetimeformat/add-all-tz.js'

if ('__setDefaultTimeZone' in Intl.DateTimeFormat) {


This library is fully test262-compliant.