Array.prototype.toLocaleString()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The toLocaleString() method of 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.

Description

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: The locales or options arguments do not control the separator used between array elements; they are simply passed to the toLocaleString() method of each element. The actual separator (usually a comma) depends solely on the host's current locale. If you expect localized list formatting, consider using Intl.ListFormat instead.

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 generic. It only expects the this value to have a length property and integer-keyed properties.

Examples

Using locales and options

The elements of the array are converted to strings using their toLocaleString methods. For example, this snippet implicitly calls the 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"

List separators

The list separator is not affected by the locales parameter. To configure it, use Intl.Locale instead.

const nums = [8888, 9999];
console.log(nums.toLocaleString("zh")); // "8,888,9,999"

const formatter = new Intl.ListFormat("zh", {
  type: "conjunction",
  style: "narrow",
});
console.log(formatter.format(nums.map((x) => x.toLocaleString("zh"))));
// "8,888、9,999"

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