Like caseFirst, numeric represents a modification to the collation rules utilized by the locale. numeric is a boolean value, which means that it can be either true or false. If numeric is set to false, there will be no special handling of numeric values in strings. If numeric is set to true, then the locale will take numeric characters into account when collating strings. This special numeric handling means that sequences of decimal digits will be compared as numbers. For example, the string "A-21" will be considered less than "A-123".

In the Unicode locale string spec, the values that numeric represents correspond to the key kn. kn is considered a locale string "extension subtag". These subtags add additional data about the locale, and are added to locale identifiers by using the -u extension key. Thus, the numeric value can be added to the initial locale identifier string that is passed into the Intl.Locale() constructor. To set the numeric value, first add the -u extension key to the string. Next, add the -kn extension key to indicate that you are adding a value for numeric. Finally, add the numeric value to the string. If you want to set numeric to true, adding the kn key will suffice. To set the value to false, you must specify in by adding "false" after the kn key.

const locale = new Intl.Locale("fr-Latn-FR-u-kn-false");
console.log(locale.numeric); // Prints "false"

The Intl.Locale() constructor has an optional configuration object argument, which can be used to pass extension types. Set the numeric property of the configuration object to your desired numeric value and pass it into the constructor.

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

• Intl.Locale