function convertNumber(num) {
    if (isNaN(num)) {
        return "Please enter a valid number.";
    }

    return {
        binary: num.toString(2), 
        decimal: num.toString(10),
        hexadecimal: num.toString(16).toUpperCase() 
    };
}

const number = 255;
console.log(convertNumber(number));

{
    "binary"; "11111111",
    "decimal"; "255",
    "hexadecimal"; "FF"
}