Letter → Next Letter And Capitalize Vowels

This code still doesn't seem to be working. It has no errors anymore, but it only returns blank brackets like this {}. It is supposed to turn each letter in str into the next lette

Solution 1:

It looks like this method can by simplified to just a few calls to .replace:

functionLetterChanges(str) { 
    return str
        .replace(/[a-y]|(z)/gi, function(c, z) { return z ? 'a' : String.fromCharCode(c.charCodeAt(0)+1); })
        .replace(/[aeiou]/g, function(c) { return x.toUpperCase(); });
}

LetterChanges("abcdefgxyz"); 
//            "bcdEfghyzA"

Or alternatively, a single call to .replace, like this:

functionLetterChanges(str) { 
    return str.replace(/(z)|([dhnt])|[a-y]/gi, function(c, z, v) {
        c = z ? 'A' : String.fromCharCode(c.charCodeAt(0)+1); 
        return v ? c.toUpperCase() : c; 
    })
}

LetterChanges("abcdefgxyz"); 
//            "bcdEfghyzA"