Web/JavaScript/Reference/Global objects/Intl/Locale/caseFirst

The Intl.Locale.prototype.caseFirst property is an accessor property that returns whether case is taken into account for the locale's collation rules.

Description

A locale's collation rules are used to determine how strings are ordered in that locale. Certain locales use a character's case (UPPERCASE or lowercase) in the collation process. This additional rule can be expressed in a Locale's caseFirst property.

There are 3 values that the caseFirst property can have, outlined in the table below.

caseFirst values

Value	Description
upper	Upper case to be sorted before lower case.
lower	Lower case to be sorted before upper case.
false	No special case ordering.

Examples

Setting the caseFirst value via the locale string

In the Unicode locale string spec, the values that caseFirst represents correspond to the key kf. kf is treated as 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 caseFirst value can be added to the inital locale identifier string that is passed into the Locale constructor. To add the caseFirst value, first add the -u extension key to the string. Next, add the -kf extension key to indicate that you are adding a value for caseFirst. Finally, add the caseFirst value to the string.

let caseFirstStr = new Intl.Locale("fr-Latn-FR-u-kf-upper");
console.log(caseFirstStr.caseFirst); // Prints "upper"

Setting the caseFirst value via the configuration object argument

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

let caseFirstObj= new Intl.Locale("en-Latn-US", {caseFirst: "lower"});
console.log(us12hour.caseFirst); // Prints "lower"

Specifications

Specification
ECMAScript Internationalization API (ECMA-402)

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
caseFirst	Chrome Full support 74	Edge Full support 79	Firefox Full support 75	IE No support No	Opera Full support 62	Safari Full support 14	WebView Android Full support 74	Chrome Android Full support 74	Firefox Android No support No	Opera Android Full support 53	Safari iOS Full support 14	Samsung Internet Android Full support 11.0	nodejs Full support 12.0.0 Notes' Full support 12.0.0 Notes' Notes' Before version 13.0.0, only the locale data for en-US is available by default. See the Locale() constructor for more details.

Legend

Full support  

Full support

No support  

No support

See implementation notes.'

See implementation notes.

See also

• Intl.Locale
• Unicode case first collation spec

Intl.Locale.prototype.caseFirst by Mozilla Contributors is licensed under CC-BY-SA 2.5.