function caesarCipher(s, k) {
    const alphabets = 'abcdefghijklmnopqrstuvwxyz'
    const alLength = alphabets.length;
    let changedString = '';
    
    for (let char of s) {
        const isUpperCase = char === char.toUpperCase();
        char = char.toLowerCase();
        if (alphabets.includes(char)){
            let newIdx = (alphabets.indexOf(char) + k) % alLength;
            if (newIdx < 0) newIdx += alLength;
            let changedLetter = alphabets[newIdx];
            if (isUpperCase) {
                changedLetter = changedLetter.toLocaleUpperCase();
            }
            changedString += changedLetter;
            
        } else {
            changedString += char;
        }
    }
    return changedString;