BigInt.prototype.toLocaleString()
=================================

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.

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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.

Try it
------

Syntax
------


```js
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` 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 with time, language, and implementation — output variations are by design and allowed by the specification. You should not compare the results of `toLocaleString()` to static values.

Examples
--------

### Using toLocaleString()

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


```js
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:


```js
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:


```js
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` parameter:


```js
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
--------------

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

Browser compatibility
---------------------

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See also
--------

* `Intl.NumberFormat`
* `BigInt.prototype.toString()`