Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2020.

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.

Every time toLocaleString is called, it has to perform a search in a big database of localization strings, which is potentially inefficient. When the method is called many times with the same arguments, it is better to create a Intl.NumberFormat object and use its format() method, because a NumberFormat object remembers the arguments passed to it and may decide to cache a slice of the database, so future format calls can search for localization strings within a more constrained context.

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toLocaleString(locales, options)


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 Optional

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 Optional

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 representing the given BigInt according to language-specific conventions.

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

Note: Most of the time, the formatting returned by toLocaleString() is consistent. However, the output may vary between implementations, even within the same locale — output variations are by design and allowed by the specification. It may also not be what you expect. For example, the string may use non-breaking spaces or be surrounded by bidirectional control characters. You should not compare the results of toLocaleString() to hardcoded constants.


Using toLocaleString()

Basic use of this method without specifying a locale returns a formatted string in the default locale and with default options.

const bigint = 3500n;

// "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
// 123.456.789.123.456.789

// Arabic in most Arabic speaking countries uses Eastern Arabic digits
// ١٢٣٬٤٥٦٬٧٨٩٬١٢٣٬٤٥٦٬٧٨٩

// India uses thousands/lakh/crore separators
// 1,23,45,67,89,12,34,56,789

// the nu extension key requests a numbering system, e.g. Chinese decimal
// 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 parameter:

const bigint = 123456789123456789n;

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

// the Japanese yen doesn't use a minor unit
  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


ECMAScript Internationalization API Specification
# sup-bigint.prototype.tolocalestring

Browser compatibility

BCD tables only load in the browser

See also