Intl.DateTimeFormat.prototype.format()

date

The date to format.

The format getter formats a date into a string according to the locale and formatting options of this Intl.DateTimeFormat object.

Use the format getter function for formatting a single date, here for Serbia:

const options = {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric",
};
const dateTimeFormat = new Intl.DateTimeFormat("sr-RS", options);
console.log(dateTimeFormat.format(new Date()));
// "недеља, 7. април 2013."

Use the format getter function for formatting all dates in an array. Note that the function is bound to the Intl.DateTimeFormat from which it was obtained, so it can be passed directly to Array.prototype.map().

const a = [new Date(2012, 8), new Date(2012, 11), new Date(2012, 3)];
const options = { year: "numeric", month: "long" };
const dateTimeFormat = new Intl.DateTimeFormat("pt-BR", options);
const formatted = a.map(dateTimeFormat.format);
console.log(formatted.join("; "));
// "setembro de 2012; dezembro de 2012; abril de 2012"

Most of the time, the formatting returned by format() is consistent. However, this might change in the future and isn't guaranteed for all the 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 format() to a static value:

let d = new Date("2019-01-01T00:00:00.000000Z");
let formattedDate = Intl.DateTimeFormat(undefined, {
  year: "numeric",
  month: "numeric",
  day: "numeric",
  hour: "numeric",
  minute: "numeric",
  second: "numeric",
}).format(d);

"1.1.2019, 01:00:00" === formattedDate;
// true in Firefox and others
// false in IE and Edge

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