String.prototype.localeCompare()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2017.
The localeCompare()
method of String
values returns a number indicating whether this string comes before, or after, or is the same as the given string in sort order. In implementations with Intl.Collator
API support, this method simply calls Intl.Collator
.
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()
method.
Try it
Syntax
localeCompare(compareString)
localeCompare(compareString, locales)
localeCompare(compareString, locales, options)
Parameters
The locales
and options
parameters customize the behavior of the function and let applications specify the language whose formatting conventions should be used.
In implementations that support the Intl.Collator
API, these parameters correspond exactly to the Intl.Collator()
constructor's parameters. Implementations without Intl.Collator
support are asked to ignore both parameters, making the comparison result returned entirely implementation-dependent — it's only required to be consistent.
compareString
-
The string against which the
referenceStr
is compared. All values are coerced to strings, so omitting it or passingundefined
causeslocaleCompare()
to compare against the string"undefined"
, which is rarely what you want. locales
Optional-
A string with a BCP 47 language tag, or an array of such strings. Corresponds to the
locales
parameter of theIntl.Collator()
constructor.In implementations without
Intl.Collator
support, this parameter is ignored and the host's locale is usually used. options
Optional-
An object adjusting the output format. Corresponds to the
options
parameter of theIntl.Collator()
constructor.In implementations without
Intl.Collator
support, this parameter is ignored.
See the Intl.Collator()
constructor for details on the locales
and options
parameters and how to use them.
Return value
A negative number if referenceStr
occurs before compareString
; positive if the referenceStr
occurs after compareString
; 0
if they are equivalent.
In implementations with Intl.Collator
, this is equivalent to new Intl.Collator(locales, options).compare(referenceStr, compareString)
.
Description
Returns an integer indicating whether the referenceStr
comes
before, after or is equivalent to the compareString
.
- Negative when the
referenceStr
occurs beforecompareString
- Positive when the
referenceStr
occurs aftercompareString
- Returns
0
if they are equivalent
Warning:
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 ECMAScript 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 case-insensitive sorting for an array.
const 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
Specifications
Specification |
---|
ECMAScript Language Specification # sec-string.prototype.localecompare |
ECMAScript Internationalization API Specification # sup-String.prototype.localeCompare |
Browser compatibility
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