$back.addEventListener('click', () => {
  const prevData = history.pop();
  if (!prevData) { // 되돌릴 게 없으면 종료
    return; 
  }
  $score.textContent = prevData.score;
  data = prevData.table;
  draw();
});

(중략)
function moveCells(direction) {

  history.push({
    table: JSON.parse(JSON.stringify(data)),
    score: $score.textContent,
  });

  (중략)
}