The toLocaleString() method of BigInt values returns a string with a language-sensitive representation of this BigInt. In implementations with Intl.NumberFormat API support, this method simply calls Intl.NumberFormat.

When formatting large numbers of numbers, it is better to create a Intl.NumberFormat object and use the function provided by its format() method.

Syntax

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

Parameters

The locales and options parameters customize the behavior of the function and let applications specify the language whose formatting conventions should be used.

In implementations that support the Intl.NumberFormat API, these parameters correspond exactly to the Intl.NumberFormat() constructor's parameters. Implementations without Intl.NumberFormat support are asked to ignore both parameters, making the locale used and the form of the string returned entirely implementation-dependent.

• locales

  • : A string with a BCP 47 language tag, or an array of such strings. Corresponds to the locales parameter of the Intl.NumberFormat() constructor.

    In implementations without Intl.NumberFormat support, this parameter is ignored and the host's locale is usually used.

• options

  • : An object adjusting the output format. Corresponds to the options parameter of the Intl.NumberFormat() constructor.

    In implementations without Intl.NumberFormat support, this parameter is ignored.

See the Intl.NumberFormat() constructor for details on these parameters and how to use them.

Return value

A string with a language-sensitive representation of the given BigInt.

In implementations with Intl.NumberFormat, this is equivalent to new Intl.NumberFormat(locales, options).format(number).

Examples

Using toLocaleString

In basic use without specifying a locale, a formatted string in the default locale and with default options is returned.

const bigint = 3500n;

console.log(bigint.toLocaleString());
// "3,500" if in U.S. English locale

Checking for support for locales and options parameters

The locales and options parameters may not be supported in all implementations, because support for the internationalization API is optional, and some systems may not have the necessary data. For implementations without internationalization support, toLocaleString() always uses the system's locale, which may not be what you want. Because any implementation that supports the locales and options parameters must support the Intl API, you can check the existence of the latter for support:

function toLocaleStringSupportsLocales() {
  return (
    typeof Intl === "object" &&
    !!Intl &&
    typeof Intl.NumberFormat === "function"
  );
}

Using locales

This example shows some of the variations in localized number formats. In order to get the format of the language used in the user interface of your application, make sure to specify that language (and possibly some fallback languages) using the locales argument:

const bigint = 123456789123456789n;

// German uses period for thousands
console.log(bigint.toLocaleString("de-DE"));
// 123.456.789.123.456.789

// Arabic in most Arabic speaking countries uses Eastern Arabic digits
console.log(bigint.toLocaleString("ar-EG"));
// ١٢٣٬٤٥٦٬٧٨٩٬١٢٣٬٤٥٦٬٧٨٩

// India uses thousands/lakh/crore separators
console.log(bigint.toLocaleString("en-IN"));
// 1,23,45,67,89,12,34,56,789

// the nu extension key requests a numbering system, e.g. Chinese decimal
console.log(bigint.toLocaleString("zh-Hans-CN-u-nu-hanidec"));
// 一二三,四五六,七八九,一二三,四五六,七八九

// when requesting a language that may not be supported, such as
// Balinese, include a fallback language, in this case Indonesian
console.log(bigint.toLocaleString(["ban", "id"]));
// 123.456.789.123.456.789

Using options

The results provided by toLocaleString can be customized using the options argument:

const bigint = 123456789123456789n;

// request a currency format
console.log(
  bigint.toLocaleString("de-DE", { style: "currency", currency: "EUR" }),
);
// 123.456.789.123.456.789,00 €

// the Japanese yen doesn't use a minor unit
console.log(
  bigint.toLocaleString("ja-JP", { style: "currency", currency: "JPY" }),
);
// ￥123,456,789,123,456,789

// limit to three significant digits
console.log(bigint.toLocaleString("en-IN", { maximumSignificantDigits: 3 }));
// 1,23,00,00,00,00,00,00,000

Specifications

Browser compatibility

See also

• BigInt.prototype.toString