code.js

// helloWorld function 
function helloWorld() {
    return "Hello, World!";
}

// sayHello function
function sayHello(name) {
    if(typeof name === `boolean`) {
        return `Hello, World!`
    } else {
        return `Hello, ` + name + `!`;
    }
}

function isFive(input) {
    return input == `5`
}

function isEven(input) {
    return (input % 2 === 0) && (typeof input !== `boolean`)
}

function isVowel(input) {
     if(input === `a` || input === `A` || input === `e` ||input ===  `E` || input === `i` || input === `I` || input === `o` || input === `O` || input === `u` || input === `U`) {
         return true;
     } else {
         return false
     }
}

function add(x , y) {
    if((isNaN(x) === true) || (isNaN(y) === true)) {
        return NaN;
    } else {
        return parseInt(x) + parseInt(y);
    }
}

console.log(add(`banana`,`split`));
console.log(typeof (`NaN`,4));