prevent-keyevents.html

<!DOCTYPE html>
<html>
<body>
<div>Test page to test key events being blocked by the page using Event.preventDefault(). Make sure the page has focus then press a few keys and observe behaviour (KeyEvents are reported in the terminal).</div>
</body>
<script>
function keyEventHandler(e) {
  console.log(e);
  e.preventDefault();
}
document.body.addEventListener('keydown', keyEventHandler);
</script>
</html>