intl-locales-supported/src/index.ts

Utility to help you polyfill the Node.js runtime when the Intl APIs are missing, or if the built-in Intl is missing locale data that you need.

/*
 * Copyright 2015, Yahoo Inc.
 * Copyrights licensed under the New BSD License.
 * See the accompanying LICENSE file for terms.
 */

type IntlConstructor = {
  supportedLocalesOf(locales: string | string[], options?: any): string[];
};

export default function areIntlLocalesSupported(
  locales: string | string[],
  constructorsToCheck?: Array<IntlConstructor>
): boolean {
  if (typeof Intl === 'undefined') {
    return false;
  }

  if (!locales) {
    throw new Error('locales must be supplied.');
  }

  if (!Array.isArray(locales)) {
    locales = [locales];
  }

  let intlConstructors = constructorsToCheck || [
    Intl.DateTimeFormat,
    Intl.NumberFormat,
    Intl.PluralRules,
  ];

  intlConstructors = intlConstructors.filter(Boolean);

  if (
    intlConstructors.length === 0 ||
    (constructorsToCheck &&
      intlConstructors.length !== constructorsToCheck.length)
  ) {
    return false;
  }

  return intlConstructors.every(
    intlConstructor =>
      intlConstructor.supportedLocalesOf(locales).length === locales.length
  );
}