How do I correctly use setInterval and clearInterval to switch between two different functions?

Question

For practice I am trying to display a number that increments from 0 - 9, then decrements from 9 - 0, and infinitely repeats.

The code that I have so far seems to

Answer 1

@Claude, you are right, the other solution I proposed was too different from original code. This is another possible solution, using setInterval and switching functions:

function onloadFunctions() {
    var count = 0;
    var refId = null;
    var target = document.getElementById("aux");

    var countUp = function() {
        target.innerHTML = count;
        count ++;
        if(count >= 9) {
            window.clearInterval(refId);
            refId = window.setInterval(countDown, 500);
        }
    }

    var countDown = function() {
        target.innerHTML = count;
        count --;
        if(count <= 0) {
            window.clearInterval(refId);
            refId = window.setInterval(countUp, 500);
        }
    }
    refId = window.setInterval(countUp, 500);
}