Returns a string where all alphabetic characters have been converted to uppercase, taking into account the host environment’s current locale.
var hello = "wOrLd"; var foobar = hello.toLocaleUpperCase(); console.log(hello); // "wOrLd" console.log(foobar); // "WORLD"
The required stringVar reference is a String object or string literal.
The toLocaleUpperCase method converts the characters in a string, taking into account the host environment’s current locale. In most cases, the result is the same as the result the toUpperCase method. Results differ if the rules for a language conflict with the regular Unicode case mappings, such as Turkish.
Microsoft Developer Network: Article