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 Intl page. The following Unicode extension key is allowed:

nu

The numbering system to be used. Possible values include: "arab", "arabext", "bali", "beng", "deva", "fullwide", "gujr", "guru", "hanidec", "khmr", "knda", "laoo", "latn", "limb", "mlym", "mong", "mymr", "orya", "tamldec", "telu", "thai", "tibt".

Optional. An object with some or all of the following properties:

localeMatcher

The locale matching algorithm to use. Possible values are "lookup" and "best fit"; the default is "best fit". For information about this option, see the Intl page.

style

The formatting style to use. Possible values are "decimal" for plain number formatting, "currency" for currency formatting, and "percent" for percent formatting; the default is "decimal".

currency

The currency to use in currency formatting. Possible values are the ISO 4217 currency codes, such as "USD" for the US dollar, "EUR" for the euro, or "CNY" for the Chinese RMB — see the Current currency & funds code list. There is no default value; if the style is "currency", the currency property must be provided.

currencyDisplay

How to display the currency in currency formatting. Possible values are "symbol" to use a localized currency symbol such as €, "code" to use the ISO currency code, "name" to use a localized currency name such as "dollar"; the default is "symbol".

useGrouping

Whether to use grouping separators, such as thousands separators or thousand/lakh/crore separators. Possible values are true and false; the default is true.

The following properties fall into two groups: minimumIntegerDigits, minimumFractionDigits, and maximumFractionDigits in one group, minimumSignificantDigits and maximumSignificantDigits in the other. If at least one property from the second group is defined, then the first group is ignored.

minimumIntegerDigits

The minimum number of integer digits to use. Possible values are from 1 to 21; the default is 1.

minimumFractionDigits

The minimum number of fraction digits to use. Possible values are from 0 to 20; the default for plain number and percent formatting is 0; the default for currency formatting is the number of minor unit digits provided by the ISO 4217 currency code list (2 if the list doesn't provide that information).

maximumFractionDigits

The maximum number of fraction digits to use. Possible values are from 0 to 20; the default for plain number formatting is the larger of minimumFractionDigits and 3; the default for currency formatting is the larger of minimumFractionDigits and the number of minor unit digits provided by the ISO 4217 currency code list (2 if the list doesn't provide that information); the default for percent formatting is the larger of minimumFractionDigits and 0.

minimumSignificantDigits

The minimum number of significant digits to use. Possible values are from 1 to 21; the default is 1.

maximumSignificantDigits

The maximum number of significant digits to use. Possible values are from 1 to 21; the default is 21.