The locales and options arguments 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).

In basic use without specifying a locale, a formatted string in the default locale and with default options is returned.

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 arguments are not supported in all browsers yet. To check whether an implementation supports them already, you can use the requirement that illegal language tags are rejected with a RangeError exception:

function toLocaleStringSupportsLocales() {
  try {
    new Date().toLocaleString('i');
  } catch (e) {
    return e.name === 'RangeError';
  }
  return false;
}

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 argument:

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"

Most of the time, the formatting returned by toLocaleString() is consistent. However, this might change in the future, and isn't guaranteed for all languages; output variations are by design, and allowed by the specification.

Most notably, the IE and Edge browsers insert bidirectional control characters around dates, so the output text will flow properly when concatenated with other text.

For this reason, you cannot expect to be able to compare the results of toLocaleString() to a static value:

"1/1/2019, 01:00:00" === new Date("2019-01-01T01:00:00Z").toLocaleString("en-US");
// true in Firefox and others
// false in IE and Edge

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