A numeral system is a system for expressing numbers. The numberingSystem property's value is set at construction time, either through the nu key of the locale identifier or through the numberingSystem option of the Intl.Locale() constructor. The latter takes priority if they are both present; and if neither is present, the property has value undefined.

For a list of supported numbering system types, see Intl.Locale.prototype.getNumberingSystems().

Like other locale subtags, the numbering system type can be added to the Intl.Locale object via the locale string, or a configuration object argument to the constructor.

In the Unicode locale string spec, numbering system types are locale key "extension subtags". These subtags add additional data about the locale, and are added to locale identifiers by using the -u extension. Thus, the numbering system type can be added to the initial locale identifier string that is passed into the Intl.Locale() constructor. To add the numbering system type, first add the -u extension key to the string. Next, add the -nu extension to indicate that you are adding a numbering system. Finally, add the numbering system type to the string.

const locale = new Intl.Locale("fr-Latn-FR-u-nu-mong");
console.log(locale.numberingSystem); // "mong"

The Intl.Locale() constructor has an optional configuration object argument, which can contain any of several extension types, including numbering system types. Set the numberingSystem property of the configuration object to your desired numbering system type, and then pass it into the constructor.

const locale = new Intl.Locale("en-Latn-US", { numberingSystem: "latn" });
console.log(locale.numberingSystem); // "latn"

• Intl.Locale
• Intl.Locale.prototype.getNumberingSystems()
• Details on the standard Unicode numeral systems