relative-time-format/modules/resolveLocale.js

A convenient Intl.RelativeTimeFormat polyfill

import { resolveLocale as resolveLocaleForData } from './LocaleDataStore.js';

/**
 * Resolves a locale to a supported one (if any).
 * @param  {string} locale
 * @param {Object} [options] - An object that may have the following property:
 * @param {string} [options.localeMatcher="lookup"] - The locale matching algorithm to use. Possible values are "lookup" and "best fit". Currently only "lookup" is supported.
 * @return {string} [locale]
 * @example
 * // Returns "sr"
 * resolveLocale("sr-Cyrl-BA")
 * // Returns `undefined`
 * resolveLocale("xx-Latn")
 */
export default function resolveLocale(locale) {
  var options = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
  var localeMatcher = options.localeMatcher || 'lookup';
  switch (localeMatcher) {
    case 'lookup':
      return resolveLocaleLookup(locale);
    // "best fit" locale matching is not supported.
    // https://github.com/catamphetamine/relative-time-format/issues/2
    case 'best fit':
      // return resolveLocaleBestFit(locale)
      return resolveLocaleLookup(locale);
    default:
      throw new RangeError("Invalid \"localeMatcher\" option: ".concat(localeMatcher));
  }
}

/**
 * Resolves a locale to a supported one (if any).
 * Starts from the most specific locale and gradually
 * falls back to less specific ones.
 * This is a basic implementation of the "lookup" algorithm.
 * https://tools.ietf.org/html/rfc4647#section-3.4
 * @param  {string} locale
 * @return {string} [locale]
 * @example
 * // Returns "sr"
 * resolveLocaleLookup("sr-Cyrl-BA")
 * // Returns `undefined`
 * resolveLocaleLookup("xx-Latn")
 */
export function resolveLocaleLookup(locale) {
  var resolvedLocale = resolveLocaleForData(locale);
  if (resolvedLocale) {
    return resolvedLocale;
  }
  // `sr-Cyrl-BA` -> `sr-Cyrl` -> `sr`.
  var parts = locale.split('-');
  while (locale.length > 1) {
    parts.pop();
    locale = parts.join('-');
    var _resolvedLocale = resolveLocaleForData(locale);
    if (_resolvedLocale) {
      return _resolvedLocale;
    }
  }
}
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