dateformat.js

function getDateFields(plainDateTime, locale='en-US') {
	const formatter = new Intl.DateTimeFormat(locale, {
		year: 'numeric', month: 'numeric', day: 'numeric',
		hour: 'numeric', minute: 'numeric', second: 'numeric',
		weekday: 'long',
		timeZoneName: 'short',
		dayPeriod: 'short',
		hour12: false,
	});

  return formatter
    .formatToParts(plainDateTime)
    .reduce((result, { type, value }) => {
      if (type !== 'literal') {
        result[type] = value;
      }
      return result;
    }, {});

}

function dateFormat(date, locale = 'en-US') {
	const fields = getDateFields(date, locale);
	return (strings) => {
		return strings.reduce((out, str) => {
			return str.replace(/%\{(year|month|day|hour|minute|second)\}/g, (match, name) => {
				if (name in fields) return fields[name];
				return name;
			})
		}, '');
	}
}

const formatter = dateFormat(new Date(), 'hu-HU');
console.log(formatter`%{year}-%{month}-%{day} %{hour}:%{minute}:%{second}`)