Array.prototype.toLocaleString() - JavaScript

Array.prototype.entries()
Array.prototype.find()
Array.prototype.flat()
Array.prototype.indexOf()
Array.prototype.map()
Array.prototype.reduceRight()
Array.prototype.some()
Array.prototype.toReversed()
Array.prototype.unshift()
Array: length
Function.prototype.bind()
Function: displayName Non-standard
Function.prototype.arguments Non-standard Deprecated
Function.prototype.caller Non-standard Deprecated

Instance methods

Object.prototype.__defineGetter__() Deprecated
Object.prototype.__defineSetter__() Deprecated
Object.prototype.__lookupGetter__() Deprecated
Object.prototype.__lookupSetter__() Deprecated
Object.prototype.toLocaleString()
Object.prototype.__proto__ Deprecated
Array instances returns a string representing the elements of the array. The elements are converted to strings using their toLocaleString methods and these strings are separated by a locale-specific string (such as a comma ",").

Try it

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

console.log(localeString);
/ Expected output: "1,a,12/21/1997, 2:12:00 PM",
/ This assumes "en" locale and UTC timezone - your results may vary

Syntax

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

Parameters

locales Optional: A string with a BCP 47 language tag, or an array of such strings. For the general form and interpretation of the locales argument, see the parameter description on the Intl main page.
options Optional: An object with configuration properties. What you can pass here depends on what elements are being converted. For example, for numbers, see Number.prototype.toLocaleString().

Return value

A string representing the elements of the array.

The Array.prototype.toLocaleString method traverses its content, calling the toLocaleString method of every element with the locales and options parameters provided, and concatenates them with an implementation-defined separator (such as a comma ","). Note that the method itself does not consume the two parameters — it only passes them to the toLocaleString() of each element. The choice of the separator string depends on the host's current locale, not the locales parameter.

If an element is undefined, null, it is converted to an empty string instead of the string "null" or "undefined".

When used on sparse arrays, the toLocaleString() method iterates empty slots as if they have the value undefined.

The toLocaleString() method is Number.prototype.toLocaleString() method to display the currency for the strings and numbers in the prices array:

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

/ "￥7,￥500,￥8,123,￥12"

Using toLocaleString() on sparse arrays

toLocaleString() treats empty slots the same as undefined and produces an extra separator:

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

Calling toLocaleString() on non-array objects

The toLocaleString() method reads the length property of this and then accesses each property whose key is a nonnegative integer less than length.

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

Specifications

Specification
ECMAScript® 2026 Internationalization API Specification # sup-array.prototype.tolocalestring