There are 2 main types of time keeping conventions (clocks) used around the world: the 12 hour clock and the 24 hour clock. The hourCycle property's value is set at construction time, either through the hc key of the locale identifier or through the hourCycle 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 hour cycle types, see Intl.Locale.prototype.getHourCycles().

The set accessor of hourCycle is undefined. You cannot change this property directly.

Like other locale subtags, the hour cycle 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, hour cycle 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 hour cycle type can be added to the initial locale identifier string that is passed into the Intl.Locale() constructor. To add the hour cycle type, first add the -u extension key to the string. Next, add the -hc extension to indicate that you are adding an hour cycle. Finally, add the hour cycle type to the string.

const locale = new Intl.Locale("fr-FR-u-hc-h23");
console.log(locale.hourCycle); // "h23"

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

const locale = new Intl.Locale("en-US", { hourCycle: "h12" });
console.log(locale.hourCycle); // "h12"

• Intl.Locale
• Intl.Locale.prototype.getHourCycles()
• Unicode Hour Cycle Identifier in the Unicode locale data markup language spec