Number Modification JS Fundamentals

function numberModification(num) {
    let digits = num.toString().split('');
    let average = 0;
    while (average <= 5) {
        average = 0;
        for (let i = 0; i < digits.length; i++) {
            average += parseInt(digits[i]);
        }
        average /= digits.length;
        if (average <= 5) {
            num = parseInt(num + "9");
            digits = num.toString().split('');
        }
    }
    console.log(num);
}