String.prototype.localeCompare()

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.

Syntax

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

Parameters

compareString
The string against which the referring string is compared

The locales and options arguments customize the behavior of the function and let applications specify the language whose formatting conventions should be used. In implementations, which ignore the locales and options arguments, the locale used and the form of the string returned are entirely implementation dependent.

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

Return value

A negative number if the reference string occurs before the compare string; positive if the reference string occurs after the compare string; 0 if they are equivalent.

Description

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

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

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.

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 a case-insensitive sort of an array.

var 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

Performance

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.

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'String.prototype.localeCompare' in that specification.
ECMAScript Internationalization API (ECMA-402)
The definition of 'String.prototype.localeCompare' in that specification.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
localeCompareChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 7Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
localesChrome Full support 24Edge Full support 12Firefox Full support 29IE Full support 11Opera Full support 15Safari Full support 10WebView Android No support NoChrome Android Full support 26Firefox Android No support NoOpera Android No support NoSafari iOS Full support 10Samsung Internet Android Full support 1.5nodejs ?
optionsChrome Full support 24Edge Full support 12Firefox Full support 29IE Full support 11Opera Full support 15Safari Full support 10WebView Android No support NoChrome Android Full support 26Firefox Android No support NoOpera Android No support NoSafari iOS Full support 10Samsung Internet Android Full support 1.5nodejs ?

Legend

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Compatibility unknown  
Compatibility unknown

See also