Converts all characters in this string to upper case.
If the string is already in all upper case, this method returns this.
'alphabet'.toUpperCase(); // 'ALPHABET'
'ABC'.toUpperCase(); // 'ABC'
This function uses the language independent Unicode mapping and thus only works in some languages.
Source
// TODO(floitsch): document better. (See EcmaScript for description).
String toUpperCase();