Sum all the digits of a number Javascript

Question

I am newbie.

I want to make small app which will calculate the sum of all the digits of a number.

For example, if I have the number 2568, the app will calcul

Answer 1

The sum of digits can be calculated using that function (based on other answers):

function sumDigits(n) {
    let sum = 0;
    while (n) {
        digit = n % 10;
        sum += digit;
        n = (n - digit) / 10;
    }
    return sum;
}

If you really need to sum the digits recursively there is recursive version of the function:

function sumDigitsRecursively(n) {
    let sum = sumDigits(n);
    if (sum < 10)
        return sum;
    else
        return sumDigitsRecursively(sum);
}

The sumDigitsRecursively(2568) expression will be equal to 3. Because 2+5+6+8 = 21 and 2+1 = 3.

Note that recursive solution by @FedericoAntonucci should be more efficient, but it does not give you intermediate sum of digits if you need it.