JavaScript (ES2026) reference · String Methods

JavaScript String toLocaleUpperCase() Method

Convert to uppercase using a language's rules, for example Turkish or German special cases.

JavaScript (ES2026) Since ES3

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Syntax

string.toLocaleUpperCase(locales)

Parameter	Description
`locales` optional	A locale such as `"tr"` or `"de"`.

A new string.

Turkish dotted ITry it yourself

console.log("i".toUpperCase(), "i".toLocaleUpperCase("tr"));

Output

I İ

German sharp sTry it yourself

console.log("straße".toLocaleUpperCase("de"));

Output

STRASSE

Version	Change
JavaScript ES3	Added

string.toUpperCase() · Return the string converted to uppercase letters. Use toLocaleUpperCase() for language-specific rules.
string.toLocaleLowerCase() · Convert to lowercase using a language's rules, which matters for languages like Turkish.
JavaScript Strings · tutorial
JavaScript String Methods · tutorial