Exercicio - transformar string

excercicio.txt

Transformar uma string em outra na qual cada letra do alfabeto deve ser a proxima mantendo o resto igual. ex: a -> b, z -> a, f -> g.
Após a transformação gerar uma nova string onde toda vogal deve ser maiúscula.

exemplos:

Input:"hello*3"

Output:"Ifmmp*3"

Input:"fun times!"

Output:"gvO Ujnft!"

transform.js

const str = "hello*3d";
const stringToArray = (str, strLength = 0, arr = []) => {
    if(strLength === str.length) return arr;
    arr.push(str[strLength])
    return stringToArray(str, strLength + 1, arr );
};
const isLetter = char => char.match(/\w/) !== null;
const isLetterZ = char => char === "z";
const isVowel = char => {
    let t = char.match(/[aeiou]/)
    return t ? t[0].toUpperCase() : char;
};
const vowelToUpper = fn => char => fn(char);
const changeLetter = char => {
        return isLetterZ(char) ? "a" : 
                    isLetter(char) ?  
                    String.fromCharCode(char.charCodeAt(0) + 1) : char;

};
const map = fn => xs => xs.map(fn);
const join = (xs, separator = "") => xs.join(separator);
const derivedWord =  map(changeLetter)(stringToArray(str));
const newWord =  map(vowelToUpper(isVowel))(derivedWord)
const finalWord = join(newWord);

https://gist.github.com/lubien/07af7b43231d7e584f4a23b0e1e175a4

https://gist.github.com/Woodsphreaker/d4f70c4c41d34cbc04629292a5bd1bda