Uppercase<S>
Converts each character in the string literal type S to uppercase.
Syntax
Uppercase<StringType>Returns
string literal type — A string literal type with every character uppercased.
Examples
type Yell = Uppercase<'hello'>; // 'HELLO'
type EventName<T extends string> = `on${Uppercase<T>}`;
type Click = EventName<'click'>; // 'onCLICK'
Notes
An intrinsic string-manipulation type implemented in the compiler. It
distributes over unions and works on template literal types. Has no runtime
representation; it only transforms types.