Array.prototype.toLocaleString()

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().

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

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"

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

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

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

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