The String toLocaleUpperCase() method

Find out all about the JavaScript toLocaleUpperCase() method of a string

Returns a new string with the uppercase transformation of the original string, according to the locale case mappings.

The first parameter represents the locale, but it’s optional (and if omitted, the current locale is used):

'Testing'.toLocaleUpperCase() //'TESTING'
'Testing'.toLocaleUpperCase('it') //'TESTING'
'Testing'.toLocaleUpperCase('tr') //'TESTİNG'

Similar to the toUpperCase() method, except that does not take locales into consideration.