I'm trying to imitate scrollTop (jQuery) in vanilla JS, so on click it scrolls to an element. This works fine - unless you have already scrolled past the element. So it doesn't scroll the opposite way. Should my formula incorporate window.pageYOffset?

var moves = function(scrollz) {

    var scrollPos = document.getElementById(scrollz).offsetTop - ((document.documentElement.clientHeight - document.getElementById(scrollz).offsetHeight) / 2);



    var timerID = setInterval(function() {

        window.scrollBy(0, speed);

        if (window.pageYOffset >= scrollPos) {

            clearInterval(timerID);

        }

    }, 13);

}