Array.prototype.toLocaleString()

const array1 = [1, "a", new Date("21 Dec 1997 14:12:00 UTC")];
const localeString = array1.toLocaleString("en", { timeZone: "UTC" });

console.log(localeString);
//   : "1,a,12/21/1997, 2:12:00 PM",
//  "en"  UTC   .      .

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

const prices = ["7", 500, 8123, 12];
prices.toLocaleString("ja-JP", { style: "currency", currency: "JPY" });

// "7,500,8,123,12"

console.log([1, , 3].toLocaleString()); // '1,,3'

const arrayLike = {
  length: 3,
  0: 1,
  1: 2,
  2: 3,
  3: 4, // length 3 toLocaleString()  
};
console.log(Array.prototype.toLocaleString.call(arrayLike));
// 1,2,3