Reddit: skok między postami klawiszami J i K

// Jump between feed posts with the J and K keys
function posts() {
  return Array.prototype.slice.call(document.querySelectorAll('shreddit-post'));
}
function current(list) {
  return list.findIndex(function (p) {
    const r = p.getBoundingClientRect();
    return r.top >= -2 && r.top < window.innerHeight / 2;
  });
}
document.addEventListener('keydown', function (e) {
  if (e.ctrlKey || e.metaKey || e.altKey) { return; }
  const tag = (e.target.tagName || '').toLowerCase();
  if (tag === 'input' || tag === 'textarea' || e.target.isContentEditable) { return; }
  if (e.key !== 'j' && e.key !== 'k') { return; }
  const list = posts();
  if (!list.length) { return; }
  let i = current(list);
  if (i < 0) { i = 0; }
  i += (e.key === 'j' ? 1 : -1);
  i = Math.max(0, Math.min(list.length - 1, i));
  list[i].scrollIntoView({ behavior: 'smooth', block: 'start' });
});