IntlDateTimeFormatlocales

Intl.DateTimeFormat is a constructor in the ECMAScript Internationalization API (ECMA-402) that formats date and time values according to a specified locale and formatting options. It enables locale-sensitive representation of dates and times, taking into account language, region, time zone, and calendar conventions.

Creation and locales: The formatter is created with new Intl.DateTimeFormat(locales, options). The locales parameter can be a string such as "en-US" or an array of locale strings. If omitted, the environment’s default locale is used. The options object can influence how components of a date and time are presented.

Formatting options: Options control which parts of the date and time are shown and how they are styled. Common options include year, month, day, weekday, hour, minute, second, timeZone, timeZoneName, era, calendar, numberingSystem, and hour12. Values such as 'numeric', '2-digit', 'long', 'short', or 'narrow' determine the level of detail and typography. The timeZone option selects a time zone like "UTC" or "America/New_York", and timeZoneName can produce a short or long designation.

Methods: The object provides format(date) to produce a localized string for a given Date, and formatToParts(date) to return a structured array of date-time parts (e.g., year, month, day, literal text). resolvedOptions() returns the resolved locale, calendar, numbering system, and other active settings for the instance.

Usage notes: Intl.DateTimeFormat is widely supported in modern browsers and Node.js (as part of ECMA-402). It is useful for producing user-friendly dates and times in multilingual applications and can be combined with supportedLocalesOf to detect locale support.