y>

<script>
var scroller = document.getElementById("scroller");
var space = document.getElementById("space");
const MAX_FRAME_COUNT = 700;
const MAX_UNCHANGED_FRAME = 20;

function scrollTop() {
  return scroller.scrollTop;
}

var scroll_arrived_after_scroll_end = false;
var scroll_end_arrived = false;
scroller.addEventListener("scroll", () => {
  if (scroll_end_arrived)
    scroll_arrived_after_scroll_end = true;
});
scroller.addEventListener("scrollend", () => {
  scroll_end_arrived = true;
});

function