1.2.6 • Public • Published
⚠️ Intl.js is no longer actively maintained, due to other commitments from the original author and maintainers. Please fork if you wish to make improvements.

Intl.js Build Status

In December 2012, ECMA International published the first edition of Standard ECMA-402, better known as the ECMAScript Internationalization API. This specification provides the framework to bring long overdue localization methods to ECMAScript implementations.

All modern browsers, have implemented this API. Intl.js fills the void of availability for this API in legacy browsers. It will provide the framework as described by the specification, so that developers can take advantage of the native API in environments that support it, or Intl.js for legacy or unsupported environments.

Getting started

Intl.js and FT Polyfill Service

Intl.js polyfill was recently added to the Polyfill service, which is developed and maintained by a community of contributors led by a team at the Financial Times. It is available through cdn.polyfill.io domain, which routes traffic through Fastly, which makes it available with global high availability and superb performance no matter where your users are.

To use the Intl polyfill through the Polyfill service just add one script tag in your page before you load or parse your own JavaScript:

<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=Intl.~locale.en"></script>

When specifying the features to use through the polyfill service, you have to specify what locale, or locales to load along with the Intl polyfill for the page to function, in the example above we are specifying Intl.~locale.en, which means only en, but you could do something like this:

<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=Intl.~locale.fr,Intl.~locale.pt"></script>

note: the example above will load the polyfill with two locale data set, fr and pt.

This is by far the best option to use the Intl polyfill since it will only load the polyfill code and the corresponding locale data when it is really needed (e.g.: legacy browsers will get the code and patch the runtime while chrome will get an empty script tag).

Intl.js and Node

For Node.js applications, you can install intl using NPM:

npm install intl

Node.js 0.12 has the Intl APIs built-in, but only includes the English locale data by default. If your app needs to support more locales than English, you'll need to get Node to load the extra locale data, or use intl npm package to patch the runtime with the Intl polyfill. Node.js versions prior to 0.12 and ≥v3.1 don't provide the Intl APIs, so they require that the runtime is polyfilled.

The following code snippet uses the intl polyfill and intl-locales-supported npm packages which will help you polyfill the Node.js runtime when the Intl APIs are missing, or if the built-in Intl is missing locale data that's needed for your app:

var areIntlLocalesSupported = require('intl-locales-supported');

var localesMyAppSupports = [
    /* list locales here */

if (global.Intl) {
    // Determine if the built-in `Intl` has the locale data we need.
    if (!areIntlLocalesSupported(localesMyAppSupports)) {
        // `Intl` exists, but it doesn't have the data we need, so load the
        // polyfill and patch the constructors we need with the polyfill's.
        var IntlPolyfill    = require('intl');
        Intl.NumberFormat   = IntlPolyfill.NumberFormat;
        Intl.DateTimeFormat = IntlPolyfill.DateTimeFormat;
} else {
    // No `Intl`, so use and load the polyfill.
    global.Intl = require('intl');

Intl.js and Browserify/webpack

If you build your application using browserify or webpack, you will install intl npm package as a dependency of your application. Ideally, you will avoid loading this library if the browser supports the built-in Intl. An example of conditional usage using webpack might look like this:

function runMyApp() {
    var nf = new Intl.NumberFormat(undefined, {style:'currency', currency:'GBP'});
    document.getElementById('price').textContent = nf.format(100);
if (!global.Intl) {
    ], function (require) {
} else {

note: a similar approach can be implemented with browserify, althought it does not support require.ensure.

note: the locale data is required for the polyfill to function when using it in a browser environment, in the example above, the english (en) locale is being required along with the polyfill itself.

Intl.js and Bower

Intl.js is also available as a Bower component for the front-end:

bower install intl

Then include the polyfill in your pages as described below:

<script src="path/to/intl/Intl.js"></script>
<script src="path/to/intl/locale-data/jsonp/en.js"></script>

note: use the locale for the current user, instead of hard-coding to en.


Current progress is as follows:


  • All internal methods except for some that are implementation dependent
  • Checking structural validity of language tags
  • Canonicalizing the case and order of language subtags
  • Intl.NumberFormat
    • The Intl.NumberFormat constructor (11.1)
    • Properties of the Intl.NumberFormat Constructor (11.2)
    • Properties of the Intl.NumberFormat Prototype Object (11.3)
    • Properties of Intl.NumberFormat Instances(11.4)
  • Intl.DateTimeFormat
    • The Intl.DateTimeFormat constructor (12.1)
    • Properties of the Intl.DateTimeFormat Constructor (12.2)
    • Properties of the Intl.DateTimeFormat Prototype Object (12.3)
    • Properties of Intl.DateTimeFormat Instances(12.4)
  • Locale Sensitive Functions of the ECMAScript Language Specification
    • Properties of the Number Prototype Object (13.2)
    • Properties of the Date prototype object (13.3)

Not Implemented

  • BestFitSupportedLocales internal function
  • Implementation-dependent numbering system mappings
  • Calendars other than Gregorian
  • Support for time zones
  • Collator objects (Intl.Collator) (see below)
  • Properties of the String prototype object

A few of the implemented functions may currently be non-conforming and/or incomplete.
Most of those functions have comments marked as 'TODO' in the source code.

The test suite is run with Intl.Collator tests removed, and the Collator constructor removed from most other tests in the suite. Also some parts of tests that cannot be passed by a JavaScript implementation have been disabled, as well as a small part of the same tests that fail due to this bug in v8.

What about Intl.Collator?

Providing an Intl.Collator implementation is no longer a goal of this project. There are several reasons, including:

  • The CLDR convertor does not automatically convert collation data to JSON
  • The Unicode Collation Algorithm is more complicated that originally anticipated, and would increase the code size of Intl.js too much.
  • The Default Unicode Collation Element Table is huge, even after compression, and converting to a native JavaScript object would probably make it slightly larger. Server-side JavaScript environments will (hopefully) soon support Intl.Collator, and we can't really expect client environments to download this data.


Intl.js is designed to be compatible with ECMAScript 3.1 environments in order to follow the specification as closely as possible. However, some consideration is given to legacy (ES3) environments, and the goal of this project is to at least provide a working, albeit non-compliant implementation where ES5 methods are unavailable.

A subset of the tests in the test suite are run in IE 8. Tests that are not passable are skipped, but these tests are mostly about ensuring built-in function behavior.

Locale Data

Intl.js uses the Unicode CLDR locale data, as recommended by the specification. The main Intl.js file contains no locale data itself. In browser environments, the data should be provided, passed into a JavaScript object using the Intl.__addLocaleData() method. In Node.js, or when using require('intl'), the data is automatically added to the runtime and does not need to be provided.

Contents of the locale-data directory are a modified form of the Unicode CLDR data found at http://www.unicode.org/cldr/.

RegExp cache / restore

Intl.js attempts to cache and restore static RegExp properties before executing any regular expressions in order to comply with ECMA-402. This process is imperfect, and some situations are not supported. This behavior is not strictly necessary, and is only required if the app depends on RegExp static properties not changing (which is highly unlikely). To disable this functionality, invoke Intl.__disableRegExpRestore().


See the CONTRIBUTING file for info.


Copyright (c) 2013 Andy Earnshaw

This software is licensed under the MIT license. See the LICENSE.txt file accompanying this software for terms of use.

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