pure javascript scrollTop function

scrollTop.js

function scrollTo(element, to, duration) {
  if (duration < 0) return;
  var difference = to - element.scrollTop;
  var perTick = difference / duration * 2;

	setTimeout(function() {
	    element.scrollTop = element.scrollTop + perTick;
	    scrollTo(element, to, duration - 2);
	}, 10);
}

document.querySelector('.js-top-button').onclick = function () {
    scrollTo(document.body, 0, 100);
};