The toLocaleUpperCase() method of String values returns this string converted to upper case, according to any locale-specific case mappings.
Syntax
toLocaleUpperCase()
toLocaleUpperCase(locales)
Parameters
locales: A string with a BCP 47 language tag, or an array of such strings. Indicates the locale to be used to convert to upper case according to any locale-specific case mappings. For the general form and interpretation of the
localesargument, see the parameter description on theIntlmain page.Unlike other methods that use the
localesargument,toLocaleUpperCase()does not allow locale matching. Therefore, after checking the validity of thelocalesargument,toLocaleUpperCase()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 upper case, according to any locale-specific case mappings.
Description
The toLocaleUpperCase() method returns the value of the string converted
to upper case according to any locale-specific case mappings.
toLocaleUpperCase() does not affect the value of the string itself. In most
cases, this will produce the same result as toUpperCase(), 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.
Also notice that conversion is not necessarily a 1:1 character mapping, as some
characters might result in two (or even more) characters when transformed to upper-case.
Therefore the length of the result string can differ from the input length. This also
implies that the conversion is not stable, so i.E. the following can return
false:
x.toLocaleLowerCase() === x.toLocaleUpperCase().toLocaleLowerCase()
Examples
Using toLocaleUpperCase()
"alphabet".toLocaleUpperCase(); // 'ALPHABET'
"Gesäß".toLocaleUpperCase(); // 'GESÄSS'
"i\u0307".toLocaleUpperCase("lt-LT"); // 'I'
const locales = ["lt", "LT", "lt-LT", "lt-u-co-phonebk", "lt-x-lietuva"];
"i\u0307".toLocaleUpperCase(locales); // 'I'