/**
 * Intl.DisplayNames.prototype.resolvedOptions().type is the same as the options.type passed to Intl.DisplayNames(locales, options) constructor
 * 
 * This can be one of "calendar", "currency", "dateTimeField", "language", "region", or "script".
 */
const dnCalendar = new Intl.DisplayNames('en', {type: 'calendar'});
console.log(dnCalendar.of('roc')); // "Minguo Calendar"
console.log(dnCalendar.resolvedOptions().type); // "calendar"
const dnCurrency = new Intl.DisplayNames(['en'], {type: 'currency'});
console.log(dnCurrency.of('USD')); // "US Dollar"
console.log(dnCurrency.resolvedOptions().type); // "currency"
const dnDateTimeField = new Intl.DisplayNames('pt', {type: 'dateTimeField'});
console.log(dnDateTimeField.of('era')); // "era"
console.log(dnDateTimeField.resolvedOptions().type); // "dateTimeField"
const dnLanguage = new Intl.DisplayNames([], {type: 'language'});
console.log(dnLanguage.of('US')); // "us"
console.log(dnLanguage.resolvedOptions().type); // "language"
const dnRegion = new Intl.DisplayNames(['en'], {type: 'region'});
console.log(dnRegion.of('BZ'));  // "Belize"
console.log(dnRegion.resolvedOptions().type); // "region"
const dnScript = new Intl.DisplayNames(['en'], {type: 'script'});
console.log(dnScript.of('Latn')); // "Latin"
console.log(dnScript.resolvedOptions().type); // "script"
/**
 * Also, when options.type === "language", resolvedOptions().languageDisplay will be either "dialect" or "standard".
 * Else, resolvedOptions.languageDisplay is undefined.
 */
const dnStd = new Intl.DisplayNames('en', {type: 'language', languageDisplay: 'standard'});
console.log(dnStd.of('en-GB')); // "English (United Kingdom)"
console.log(dnStd.resolvedOptions().languageDisplay); // "standard"
console.log(dnLanguage.resolvedOptions().languageDisplay); // "dialect"
console.log(dnCurrency.resolvedOptions().languageDisplay); // undefined

/**
 * The constructor new Intl.DisplayNames(locales, options) requires options.
 * 
 * options.type is required, while all other fields are optional.
 */
// new Intl.DisplayNames(); // TypeError: invalid_argument
// new Intl.DisplayNames('en'); // TypeError: invalid_argument
// new Intl.DisplayNames('en', {}); // TypeError: invalid_argument
console.log((new Intl.DisplayNames(undefined, {type: 'language'})).of('en-GB')); // "British English"

/**
 * locales argument can be an array of both strings and Locale(s) at the same time.
 * 
 * This applies to Intl.DisplayNames(locales, options) constructor and Intl.DisplayNames.supportedLocalesOf(locales)
 */
const localesArg = ["es-ES", new Intl.Locale("en-US")];
console.log((new Intl.DisplayNames(localesArg, {type: 'language'})).resolvedOptions().locale); // "es-ES"
console.log(Intl.DisplayNames.supportedLocalesOf(localesArg)); // ["es-ES", "en-US"]
/**
 * locales, options, and options.localeMatcher are optional in Intl.DisplayNames.supportedLocalesOf(locales, options)
 */
console.log(Intl.DisplayNames.supportedLocalesOf()); // []
console.log(Intl.DisplayNames.supportedLocalesOf(localesArg, {})); // ["es-ES", "en-US"]