Date.prototype.toLocaleString()

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

// British English uses day-month-year order and 24-hour time without AM/PM
console.log(event.toLocaleString("en-GB", { timeZone: "UTC" }));
// Expected output: "20/12/2012, 03:00:00"

// Korean uses year-month-day order and 12-hour time with AM/PM
console.log(event.toLocaleString("ko-KR", { timeZone: "UTC" }));
// Expected output: "2012. 12. 20.  3:00:00"

toLocaleString()
toLocaleString(locales)
toLocaleString(locales, options)

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

//   toLocaleString()  ,  ,    
console.log(date.toLocaleString());
//  "12/11/2012, 7:00:00 PM" en-Us   America/Los_Angeles   

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

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

//      
// America/Los_Angeles for the US

//   --  AM/PM  12 
console.log(date.toLocaleString("en-US"));
//  "12/19/2012, 7:00:00 PM"

//   --  AM/PM  24 
console.log(date.toLocaleString("en-GB"));
//  "20/12/2012 03:00:00"

//  --  AM/PM  12 
console.log(date.toLocaleString("ko-KR"));
//  "2012. 12. 20.  12:00:00"

//        
console.log(date.toLocaleString("ar-EG"));
//  "// :: "

//  ,       
// 2012  Heisei 24 
console.log(date.toLocaleString("ja-JP-u-ca-japanese"));
//  "24/12/20 12:00:00"

//         ,   . (  )
console.log(date.toLocaleString(["ban", "id"]));
//  "20/12/2012 11.00.00"

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"

//  UTC        .
options.timeZone = "UTC";
options.timeZoneName = "short";

console.log(date.toLocaleString("en-US", options));
//  "Thursday, December 20, 2012, GMT"

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

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