The localeCompare() method returns a number indicating whether a reference string comes before or after or is the same as the given string in sort order.

The new locales and options arguments let applications specify the language whose sort order should be used and customize the behavior of the function. In older implementations, which ignore the locales and options arguments, the locale and sort order used are entirely implementation dependent.


referenceStr.localeCompare(compareString[, locales[, options]])


Check the Browser compatibility section to see which browsers support the locales and options arguments, and the Checking for support for locales and options arguments for feature detection.

The string against which the referring string is compared


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

DO NOT rely on exact return values of -1 or 1. Negative and positive integer results vary between browsers (as well as between browser versions) because the W3C specification only mandates negative and positive values. Some browsers may return -2 or 2 or even some other negative or positive value.


Using localeCompare()

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

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

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

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 with a
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


When comparing large numbers of strings, such as in sorting large arrays, it is better to create an Intl.Collator object and use the function provided by its compare property.

  Created by Mozilla Contributors, license: CC-BY-SA 2.5