Array.prototype.toLocaleString()

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 ",").

Syntax

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

Parameters

locales
- : 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
- : An object with configuration properties. For numbers, see Number.prototype.toLocaleString; for dates, see Date.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 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 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.

Object: Object.prototype.toLocaleString
Number: Number.prototype.toLocaleString
Date: Date.prototype.toLocaleString

Always 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"

For more examples, see also the Intl.NumberFormat and Intl.DateTimeFormat pages.

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