<script>

let startCoord;

window.addEventListener('mousedown', (event) => {

  startCoord = [event.clientX, event.clientY]; -------------- ①

});
window.addEventListener('mouseup', (event) => {

  const endCoord = [event.clientX, event.clientY]; ---------- ②
  const diffX = endCoord[0] - startCoord[0]; ---------------- ③
  const diffY = endCoord[1] - startCoord[1]; ---------------- ③
  const isUnder45 = Math.abs(diffX) > Math.abs(diffY); ------ ④
  if (diffX < 0 && isUnder45) { ----------------------------- ⑤
    console.log('왼쪽');
  } else if (diffX > 0 && isUnder45) {
    console.log('오른쪽');
  } else if (diffY > 0 && !isUnder45) {
    console.log('아래쪽');
  } else if (diffY < 0 && !isUnder45) {
    console.log('위쪽');
  }

});
</script>