String.prototype.localeCompare()

Try it

const a = "réservé"; // With accents, lowercase
const b = "RESERVE"; // No accents, uppercase

console.log(a.localeCompare(b));
// Expected output: 1
console.log(a.localeCompare(b, "en", { sensitivity: "base" }));
// Expected output: 0

Syntax

localeCompare(compareString)
localeCompare(compareString, locales)
localeCompare(compareString, locales, options)

Parameters

The locales and options parameters customize the behavior of the function and let applications specify the language whose formatting conventions should be used.

In implementations that support the Intl.Collator API, these parameters correspond exactly to the Intl.Collator() constructor's parameters. Implementations without Intl.Collator support are asked to ignore both parameters, making the comparison result returned entirely implementation-dependent — it's only required to be consistent.

compareString

The string against which the referenceStr is compared. All values are coerced to strings, so omitting it or passing undefined causes localeCompare() to compare against the string "undefined", which is rarely what you want.

locales Optional

A string with a BCP 47 language tag, or an array of such strings. Corresponds to the locales parameter of the Intl.Collator() constructor.

In implementations without Intl.Collator support, this parameter is ignored and the host's locale is usually used.

options Optional

An object adjusting the output format. Corresponds to the options parameter of the Intl.Collator() constructor.

In implementations without Intl.Collator support, this parameter is ignored.

See the Intl.Collator() constructor for details on the locales and options parameters and how to use them.

Return value

A negative number if referenceStr occurs before compareString; positive if the referenceStr occurs after compareString; 0 if they are equivalent.

In implementations with Intl.Collator, this is equivalent to new Intl.Collator(locales, options).compare(referenceStr, compareString).

Description

Returns an integer indicating whether the referenceStr comes before, after or is equivalent to the compareString.

• Negative when the referenceStr occurs before compareString
• Positive when the referenceStr occurs after compareString
• Returns 0 if they are equivalent

Examples

Using localeCompare()

// The letter "a" is before "c" yielding a negative value
"a".localeCompare("c"); // -2 or -1 (or some other negative value)

// Alphabetically the word "check" comes after "against" yielding a positive value
"check".localeCompare("against"); // 2 or 1 (or some other positive value)

// "a" and "a" are equivalent yielding a neutral value of zero
"a".localeCompare("a"); // 0

Sort an array

localeCompare() enables case-insensitive sorting for an array.

const items = ["réservé", "Premier", "Cliché", "communiqué", "café", "Adieu"];
items.sort((a, b) => a.localeCompare(b, "fr", { ignorePunctuation: true }));
// ['Adieu', 'café', 'Cliché', 'communiqué', 'Premier', 'réservé']

Check browser support for extended arguments

The locales and options arguments are not supported in all browsers yet.

To check whether an implementation supports them, use the "i" argument (a requirement that illegal language tags are rejected) and look for a RangeError exception:

function localeCompareSupportsLocales() {
  try {
    "foo".localeCompare("bar", "i");
  } catch (e) {
    return e.name === "RangeError";
  }
  return false;
}

Using locales

The results provided by localeCompare() vary between languages. In order to get the sort order of the language used in the user interface of your application, make sure to specify that language (and possibly some fallback languages) using the locales argument:

console.log("ä".localeCompare("z", "de")); // a negative value: in German, ä sorts before z
console.log("ä".localeCompare("z", "sv")); // a positive value: in Swedish, ä sorts after z

Using options

The results provided by localeCompare() can be customized using the options argument:

// in German, ä has a as the base letter
console.log("ä".localeCompare("a", "de", { sensitivity: "base" })); // 0

// in Swedish, ä and a are separate base letters
console.log("ä".localeCompare("a", "sv", { sensitivity: "base" })); // a positive value

Numeric sorting

// by default, "2" > "10"
console.log("2".localeCompare("10")); // 1

// numeric using options:
console.log("2".localeCompare("10", undefined, { numeric: true })); // -1

// numeric using locales tag:
console.log("2".localeCompare("10", "en-u-kn-true")); // -1

Specifications

Browser compatibility

See also

• Intl.Collator