The locales and options parameters customize the behavior of the function and let applications specify the language whose formatting conventions should be used.

In implementations that support the Intl.DateTimeFormat API, these parameters correspond exactly to the Intl.DateTimeFormat() constructor's parameters. Implementations without Intl.DateTimeFormat support are asked to ignore both parameters, making the locale used and the form of the string returned entirely implementation-dependent.

locales Optional

A string with a BCP 47 language tag, or an array of such strings. Corresponds to the locales parameter of the Intl.DateTimeFormat() constructor.

In implementations without Intl.DateTimeFormat support, this parameter is ignored and the host's locale is usually used.

options Optional

An object adjusting the output format. Corresponds to the options parameter of the Intl.DateTimeFormat() constructor. If weekday, year, month, day, dayPeriod, hour, minute, second, and fractionalSecondDigits are all undefined, then year, month, day, hour, minute, second will be set to "numeric".

In implementations without Intl.DateTimeFormat support, this parameter is ignored.

See the Intl.DateTimeFormat() constructor for details on these parameters and how to use them.

A string representing the given date according to language-specific conventions.

In implementations with Intl.DateTimeFormat, this is equivalent to new Intl.DateTimeFormat(locales, options).format(date).

Basic use of this method without specifying a locale returns a formatted string in the default locale and with default options.

const date = new Date(Date.UTC(2012, 11, 12, 3, 0, 0));

// toLocaleString() without arguments depends on the
// implementation, the default locale, and the default time zone
console.log(date.toLocaleString());
// "12/11/2012, 7:00:00 PM" if run in en-US locale with time zone America/Los_Angeles

The locales and options parameters may not be supported in all implementations, because support for the internationalization API is optional, and some systems may not have the necessary data. For implementations without internationalization support, toLocaleString() always uses the system's locale, which may not be what you want. Because any implementation that supports the locales and options parameters must support the Intl API, you can check the existence of the latter for support:

function toLocaleStringSupportsLocales() {
  return (
    typeof Intl === "object" &&
    !!Intl &&
    typeof Intl.DateTimeFormat === "function"
  );
}

This example shows some of the variations in localized date and time formats. In order to get the format of the language used in the user interface of your application, make sure to specify that language (and possibly some fallback languages) using the locales argument:

const date = new Date(Date.UTC(2012, 11, 20, 3, 0, 0));

// Formats below assume the local time zone of the locale;
// America/Los_Angeles for the US

// US English uses month-day-year order and 12-hour time with AM/PM
console.log(date.toLocaleString("en-US"));
// "12/19/2012, 7:00:00 PM"

// British English uses day-month-year order and 24-hour time without AM/PM
console.log(date.toLocaleString("en-GB"));
// "20/12/2012 03:00:00"

// Korean uses year-month-day order and 12-hour time with AM/PM
console.log(date.toLocaleString("ko-KR"));
// "2012. 12. 20. 오후 12:00:00"

// Arabic in most Arabic-speaking countries uses Eastern Arabic numerals
console.log(date.toLocaleString("ar-EG"));
// "٢٠‏/١٢‏/٢٠١٢ ٥:٠٠:٠٠ ص"

// For Japanese, applications may want to use the Japanese calendar,
// where 2012 was the year 24 of the Heisei era
console.log(date.toLocaleString("ja-JP-u-ca-japanese"));
// "24/12/20 12:00:00"

// When requesting a language that may not be supported, such as
// Balinese, include a fallback language (in this case, Indonesian)
console.log(date.toLocaleString(["ban", "id"]));
// "20/12/2012 11.00.00"

The results provided by toLocaleString() can be customized using the options parameter:

const date = new Date(Date.UTC(2012, 11, 20, 3, 0, 0));

// Request a weekday along with a long date
const options = {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric",
};
console.log(date.toLocaleString("de-DE", options));
// "Donnerstag, 20. Dezember 2012"

// An application may want to use UTC and make that visible
options.timeZone = "UTC";
options.timeZoneName = "short";
console.log(date.toLocaleString("en-US", options));
// "Thursday, December 20, 2012, GMT"

// Sometimes even the US needs 24-hour time
console.log(date.toLocaleString("en-US", { hour12: false }));
// "12/19/2012, 19:00:00"

• Intl.DateTimeFormat
• Date.prototype.toLocaleDateString()
• Date.prototype.toLocaleTimeString()
• Date.prototype.toString()