Intl.DateTimeFormat

const date = new Date(Date.UTC(2020, 11, 20, 3, 23, 16, 738));
//  UTC  - 

// Specify default date formatting for language (locale)
console.log(new Intl.DateTimeFormat("en-US").format(date));
// : "12/20/2020"

// 
console.log(new Intl.DateTimeFormat(["ban", "id"]).format(date));
// : "20/12/2020"

// "style" : full, long, medium, short
console.log(
  new Intl.DateTimeFormat("en-GB", {
    dateStyle: "full",
    timeStyle: "long",
    timeZone: "Australia/Sydney",
  }).format(date),
);
// : "Sunday, 20 December 2020 at 14:23:16 GMT+11"

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

//  toLocaleString 
// 
console.log(new Intl.DateTimeFormat().format(date));
// "12/19/2012"  en-US  America/Los_Angeles (UTC-0800) 

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

//  America/Los_Angeles (UTC-0800, ) 

//  -- 
console.log(new Intl.DateTimeFormat("en-US").format(date));
// "12/19/2012"

//  -- 
console.log(new Intl.DateTimeFormat("en-GB").format(date));
//  "19/12/2012"

//  -- 
console.log(new Intl.DateTimeFormat("ko-KR").format(date));
// "2012. 12. 19."

// 
console.log(new Intl.DateTimeFormat("ar-EG").format(date));
// "//"

//  2012  24 
console.log(new Intl.DateTimeFormat("ja-JP-u-ca-japanese").format(date));
// "24/12/19"

// 
console.log(new Intl.DateTimeFormat(["ban", "id"]).format(date));
// "19/12/2012"

const date = new Date(Date.UTC(2012, 11, 20, 3, 0, 0, 200));

// 
let options = {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric",
};
console.log(new Intl.DateTimeFormat("de-DE", options).format(date));
// "Donnerstag, 20. Dezember 2012"

//  UTC 
options.timeZone = "UTC";
options.timeZoneName = "short";
console.log(new Intl.DateTimeFormat("en-US", options).format(date));
// "Thursday, December 20, 2012, GMT"

// 
options = {
  hour: "numeric",
  minute: "numeric",
  second: "numeric",
  timeZone: "Australia/Sydney",
  timeZoneName: "short",
};
console.log(new Intl.DateTimeFormat("en-AU", options).format(date));
// "2:00:00 pm AEDT"

// 
options.fractionalSecondDigits = 3; // 
console.log(new Intl.DateTimeFormat("en-AU", options).format(date));
// "2:00:00.200 pm AEDT"

//  24 
options = {
  year: "numeric",
  month: "numeric",
  day: "numeric",
  hour: "numeric",
  minute: "numeric",
  second: "numeric",
  hour12: false,
  timeZone: "America/Los_Angeles",
};
console.log(new Intl.DateTimeFormat("en-US", options).format(date));
// "12/19/2012, 19:00:00"

// undefined 
console.log(new Intl.DateTimeFormat(undefined, options).format(date));
// "12/19/2012, 19:00:00"

// 
options = { hour: "numeric", dayPeriod: "short" };
console.log(new Intl.DateTimeFormat("en-US", options).format(date));
// 10 at night

const options = { calendar: "chinese", numberingSystem: "arab" };
const dateFormat = new Intl.DateTimeFormat(undefined, options);
const usedOptions = dateFormat.resolvedOptions();

console.log(usedOptions.calendar);
// "chinese"

console.log(usedOptions.numberingSystem);
// "arab"

console.log(usedOptions.timeZone);
// "America/New_York"