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    String.prototype.localeCompare()

    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

    referenceStr.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 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 the options property usage (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 options property or through a Unicode extension key; if both are provided, the options 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 an options property or through a Unicode extension key; if both are provided, the options 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 and false; the default is false.
    numeric
    Whether numeric collation should be used, such that "1" < "2" < "10". Possible values are true and false; the default is false. This option can be set through an options property or through a Unicode extension key; if both are provided, the options 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 an options property or through a Unicode extension key; if both are provided, the options property takes precedence. Implementations are not required to support this property.

    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

     

    // 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
    

     

    Example: 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;
    }
    

    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:

    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
    

    Example: 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. 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 Internationalization API 1.0 (ECMA-402)
    The definition of 'String.prototype.localeCompare' in that specification.
    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
    bug 864843
    Not supported Not supported Not supported

    See also

    Document Tags and Contributors

    Last updated by: bobtherobot,
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