<!doctype html>
<meta charset="utf-8">
<title>14 wheel scroll</title>
<link rel="stylesheet" href="../_style.css">
<script src="../_lib.js"></script>
<body>
<main>
  <p>Goal: scroll the box to the bottom. Page rejects raw <code>scrollTop</code> assignment without
     <code>wheel</code> events.</p>
  <div id="box" style="height:200px;overflow:auto;border:1px solid #555;background:#fff;color:#111;padding:8px">
    <div style="height:1200px">scroll me ⬇<br><br>...lots of content...</div>
  </div>
</main>
<script>
Challenge.init({ id: "wheel-scroll", instructions: "scroll the box to its bottom" });
const box = document.getElementById("box");
let wheelCount = 0, lastWheelTs = -Infinity;
box.addEventListener("wheel", (e) => { wheelCount++; lastWheelTs = e.timeStamp; Challenge.log("wheel", { dy: e.deltaY }); }, { passive: true });
box.addEventListener("scroll", () => {
  Challenge.log("scroll", { top: box.scrollTop });
  if (box.scrollTop + box.clientHeight >= box.scrollHeight - 2) {
    if (wheelCount === 0) Challenge.fail("scrolled to bottom with zero wheel events");
    else if (performance.now() - lastWheelTs > 1500) Challenge.fail("wheel events too far before final scroll");
    else Challenge.pass(`${wheelCount} wheel events accompanied scroll`);
  }
});
</script>
</body>