The toLocaleUpperCase() method returns the calling string value converted to upper case, according to any locale-specific case mappings.


str.toLocaleUpperCase([locale, locale, ...])


locale Optional
The locale parameter indicates the locale to be used to convert to upper case according to any locale-specific case mappings. If multiple locales are given in an Array, the best available locale is used. The default locale is the host environment’s current locale.

Return value

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


  • A RangeError ("invalid language tag: xx_yy") is thrown if a locale argument isn't a valid language tag.
  • A TypeError ("invalid element in locales argument") is thrown if an array element isn't of type string.


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()


Using toLocaleUpperCase()

'alphabet'.toLocaleUpperCase(); // 'ALPHABET'

'Gesäß'.toLocaleUpperCase(); // 'GESÄSS'

'i\u0307'.toLocaleUpperCase('lt-LT'); // 'I'

let locales = ['lt', 'LT', 'lt-LT', 'lt-u-co-phonebk', 'lt-x-lietuva'];
'i\u0307'.toLocaleUpperCase(locales); // 'I'


Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
toLocaleUpperCase 1 12 1 5.5 4 1.3
locale 58 12 55 6 45 10
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
toLocaleUpperCase 1 18 4 10.1 1 1.0
locale 58 58 55 42 10 7.0
toLocaleUpperCase 0.1.100
locale 13.0.0
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 for versions prior to 13, see Node.js documentation on the --with-intl option and how to provide the data.

See also

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