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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
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.
compareString
- The string against which the referring string is compared
locales
-
Optional. A string with a BCP 47 language tag, or an array of such strings. For the general form and interpretation of the
locales
argument, see the Intl page. The following Unicode extension keys are allowed:co
- Variant collations for certain locales. Possible values include:
"big5han"
,"dict"
,"direct"
,"ducet"
,"gb2312"
,"phonebk"
,"phonetic"
,"pinyin"
,"reformed"
,"searchjl"
,"stroke"
,"trad"
,"unihan"
. The"standard"
and"search"
values are ignored; they are replaced by theoptions
propertyusage
(see below). kn
- Whether numeric collation should be used, such that "1" < "2" < "10". Possible values are
"true"
and"false"
. This option can be set through anoptions
property or through a Unicode extension key; if both are provided, theoptions
property takes precedence. kf
- Whether upper case or lower case should sort first. Possible values are
"upper"
,"lower"
, or"false"
(use the locale's default). This option can be set through anoptions
property or through a Unicode extension key; if both are provided, theoptions
property takes precedence.
options
-
Optional. An object with some or all of the following properties:
localeMatcher
- The locale matching algorithm to use. Possible values are
"lookup"
and"best fit"
; the default is"best fit"
. For information about this option, see the Intl page. usage
- Whether the comparison is for sorting or for searching for matching strings. Possible values are
"sort"
and"search"
; the default is"sort"
. sensitivity
-
Which differences in the strings should lead to non-zero result values. Possible values are:
"base"
: Only strings that differ in base letters compare as unequal. Examples:a ≠ b
,a = á
,a = A
."accent"
: Only strings that differ in base letters or accents and other diacritic marks compare as unequal. Examples:a ≠ b
,a ≠ á
,a = A
."case"
: Only strings that differ in base letters or case compare as unequal. Examples:a ≠ b
,a = á
,a ≠ A
."variant"
: Strings that differ in base letters, accents and other diacritic marks, or case compare as unequal. Other differences may also be taken into consideration. Examples:a ≠ b
,a ≠ á
,a ≠ A
.
The default is
"variant"
for usage"sort"
; it's locale dependent for usage"search"
. ignorePunctuation
- Whether punctuation should be ignored. Possible values are
true
andfalse
; the default isfalse
. numeric
- Whether numeric collation should be used, such that "1" < "2" < "10". Possible values are
true
andfalse
; the default isfalse
. This option can be set through anoptions
property or through a Unicode extension key; if both are provided, theoptions
property takes precedence. Implementations are not required to support this property. caseFirst
- Whether upper case or lower case should sort first. Possible values are
"upper"
,"lower"
, or"false"
(use the locale's default); the default is"false"
. This option can be set through anoptions
property or through a Unicode extension key; if both are provided, theoptions
property takes precedence. Implementations are not required to support this property.
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
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
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 | Status | Comment |
---|---|---|
ECMAScript 3rd Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.2. |
ECMAScript 5.1 (ECMA-262) The definition of 'String.prototype.localeCompare' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'String.prototype.localeCompare' in that specification. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'String.prototype.localeCompare' in that specification. |
Draft | |
ECMAScript Internationalization API 1.0 (ECMA-402) The definition of 'String.prototype.localeCompare' in that specification. |
Standard | locale and option parameter definitions. |
ECMAScript Internationalization API 2.0 (ECMA-402) The definition of 'String.prototype.localeCompare' in that specification. |
Standard | |
ECMAScript Internationalization API 4.0 (ECMA-402) The definition of 'String.prototype.localeCompare' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
locales and options arguments |
24 | 29 (29) | 11 | 15 | 10 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
locales and options arguments |
No support | 26 | No support | No support | No support | 10 |