Summary
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
str.localeCompare(compareString [, locales [, options]])Parameters
Check the Browser compatibility section to see which browsers support the locales and options arguments, and the Example: Checking for support for locales and options arguments for feature detection.
-
compareString - The string against which the referring string is comparing
-
locales -
A string with a BCP 47 language tag, or an array of such strings. For the general form and interpretation of the
localesargument, 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 the
optionspropertyusage(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 an
optionsproperty or through a Unicode extension key; if both are provided, theoptionsproperty 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 an
optionsproperty or through a Unicode extension key; if both are provided, theoptionsproperty takes precedence.
-
options -
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
trueandfalse; the default isfalse. -
numeric -
Whether numeric collation should be used, such that "1" < "2" < "10". Possible values are
trueandfalse; the default isfalse. This option can be set through anoptionsproperty or through a Unicode extension key; if both are provided, theoptionsproperty 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 an
optionsproperty or through a Unicode extension key; if both are provided, theoptionsproperty takes precedence. Implementations are not required to support this property.
-
Description
Returns a number indicating whether a reference string comes before or after or is the same as the given string in sort order. Returns a negative number if the string occurs earlier in a sort than compareString, returns a positive number if the string occurs afterwards in such a sort, and returns 0 if they occur at the same level.
Examples
Example: Using localeCompare
The following example demonstrates the different potential results for a string occurring before, after, or at the same level as another:
alert('a'.localeCompare('c')); // -2, or -1, or some other negative value
alert('c'.localeCompare('a')); // 2, or 1, or some other positive value
alert('a'.localeCompare('a')); // 0
Note that the results shown in the code above can vary between browsers and browser versions. This is because the values are implementation-specific. That is, the specification requires only that the before and after values are negative and positive.
Example: Checking for support for locales and options arguments
The locales and options arguments are not supported in all browsers yet. To check whether an implementation supports them already, you can use the requirement that illegal language tags are rejected with a RangeError exception:
function localeCompareSupportsLocales() {
try {
"a".localeCompare("b", "i");
} catch (e) {
return e.name === "RangeError";
}
return false;
}
Example: 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:
alert('ä'.localeCompare('z', 'de')); // a negative value: in German, ä sorts with a
alert('ä'.localeCompare('z', 'sv')); // a positive value: in Swedish, ä sorts after z
Example: Using options
The results provided by localeCompare can be customized using the options argument:
// in German, ä has a as the base letter
alert('ä'.localeCompare('a', 'de', {sensitivity: "base"})); // 0
// in Swedish, ä and a are separate base letters
alert('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. | Standard | Initial definition. Implemented in JavaScript 1.2 |
| ECMAScript Language Specification 5.1th Edition (ECMA-262) | Standard | |
| ECMAScript Language Specification 6th Edition (ECMA-262) | Draft | |
| ECMAScript Internationalization API Specification, 1st Edition | Standard | locale and option parameter defintions |
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 | Not supported |
| 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 |
Not supported | 26 | Not supported |
Not supported | Not supported | Not supported |