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String.prototype.toLocaleLowerCase()

The toLocaleLowerCase() method of String values returns this string converted to lower case, according to any locale-specific case mappings.

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Syntax

toLocaleLowerCase()
toLocaleLowerCase(locales)

Parameters

locales Optional

A string with a BCP 47 language tag, or an array of such strings. Indicates the locale to be used to convert to lower case according to any locale-specific case mappings. For the general form and interpretation of the locales argument, see the parameter description on the Intl main page.

Unlike other methods that use the locales argument, toLocaleLowerCase() does not allow locale matching. Therefore, after checking the validity of the locales argument, toLocaleLowerCase() always uses the first locale in the list (or the default locale if the list is empty), even if this locale is not supported by the implementation.

Return value

A new string representing the calling string converted to lower case, according to any locale-specific case mappings.

Description

The toLocaleLowerCase() method returns the value of the string converted to lower case according to any locale-specific case mappings. toLocaleLowerCase() does not affect the value of the string itself. In most cases, this will produce the same result as toLowerCase(), but for some locales, such as Turkish, whose case mappings do not follow the default case mappings in Unicode, there may be a different result.

Examples

Using toLocaleLowerCase()

"ALPHABET".toLocaleLowerCase(); // 'alphabet'

"\u0130".toLocaleLowerCase("tr") === "i"; // true
"\u0130".toLocaleLowerCase("en-US") === "i"; // false

const locales = ["tr", "TR", "tr-TR", "tr-u-co-search", "tr-x-turkish"];
"\u0130".toLocaleLowerCase(locales) === "i"; // true

Specifications

Specification
ECMAScript Language Specification # sec-string.prototype.tolocalelowercase
ECMAScript Internationalization API Specification # sup-string.prototype.tolocalelowercase

Browser compatibility

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	Deno	Node.js
`toLocaleLowerCase`	1	12	1	4	1.3	18	4	10.1	1	1.0	4.4	1.0	0.10.0
`locale`	58	12	55	45	10	58	55	43	10	7.0	58	1.8 1.0–1.8 Only the locale data for `en-US` is available.	13.0.0 0.12.0 Before version 13.0.0, only the locale data for `en-US` is available by default. When other locales are specified, the function silently falls back to `en-US`. To make full ICU (locale) data available before version 13, see Node.js documentation on the `--with-intl` option and how to provide the data.