A spec-compliant ponyfill for Intl.LocaleMatcher. Since this is only stage-1 this package is a ponyfill instead of polyfill.

Installation#

npm i @formatjs/intl-localematcher

Requirements#

• Intl.getCanonicalLocales or polyfill
• Intl.Locale or polyfill

Usage#

Simple#

match(['fr-XX', 'en'], ['fr', 'en'], 'en') // 'fr'

match(['zh'], ['fr', 'en'], 'en') // 'en'

Supported locale filtering#

LookupSupportedLocales(availableLocales, requestedLocales) returns supported requested tags in their original order, preserving region subtags and Unicode extensions even when matching falls back to a parent locale.

LookupSupportedLocales(['de'], ['de-AT-u-co-phonebk']) // ['de-AT-u-co-phonebk']

Locale resolution uses an internal record isolated from inherited extension-key setters on Object.prototype.

Locale matching extracts only the Unicode u extension. Private-use subtags remain intact, including text resembling u-co-phonebk; trailing extensions are preserved separately from Unicode keywords.