sanks

mandatory = () => {
  throw new Error('Missing parameter!');
}

foo = (bar = mandatory()) => {
  return bar;
}

sanks

ymaps.ready(function () {
	ymaps.geolocation.get({ provider: 'yandex' }).then(function(result) {
	  
		var data = result.geoObjects.get(0).properties.get('metaDataProperty').GeocoderMetaData;
		var administrativeAreaName = data.AddressDetails.Country.AdministrativeArea.AdministrativeAreaName; // region
		
		if ('SubAdministrativeArea' in data.AddressDetails.Country.AdministrativeArea) {
			var localityName = data.AddressDetails.Country.AdministrativeArea.SubAdministrativeArea.Locality.LocalityName; // city
		} else {
			var localityName = data.AddressDetails.Country.AdministrativeArea.Locality.LocalityName; // city