Caesars Cipher

cipher.js

function rot13(str) { // LBH QVQ VG!
var newArr = [];
var final = [];

for (var i = 0; i < str.length; i++) {
    newArr[i] = (str.charCodeAt(i));

    if (newArr[i] >= 65 && newArr[i] <= 77) {
        newArr[i] += 13;
    }
    else if (newArr[i] >=78 && newArr[i] <= 90) {
        newArr[i] -= 13;
    }
final[i] = String.fromCharCode(newArr[i]);
}
return final.join('');
}

console.log(rot13("LBH QVQ VG!"));