Array.prototype.toLocaleString()

Try it

const array = [1, "a", new Date("21 Dec 1997 14:12:00 UTC")];
const localeString = array.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 ",").

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.ListFormat 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

Browser compatibility

See also

• Indexed collections guide
• Array
• Array.prototype.toString()
• TypedArray.prototype.toLocaleString()
• Intl
• Intl.ListFormat
• Object.prototype.toLocaleString()
• Number.prototype.toLocaleString()
• Temporal.PlainDate.prototype.toLocaleString()