Native JS swipe detection

swipeDetection.js

let startX = 0;
let startY = 0;

function handleTouchStart(e) {
  startX = e.changedTouches[0].screenX;
  startY = e.changedTouches[0].screenY;
}

function handleTouchEnd(e) {
  const diffX = e.changedTouches[0].screenX - startX;
  const diffY = e.changedTouches[0].screenY - startY;
  const ratioX = Math.abs(diffX / diffY);
  const ratioY = Math.abs(diffY / diffX);
  const absDiff = Math.abs(ratioX > ratioY ? diffX : diffY);

  // Ignore small movements.
  if (absDiff < 30) {
    return;
  }

  if (ratioX > ratioY) {
    if (diffX >= 0) {
      console.log('right swipe');
    } else {
      console.log('left swipe');
    }
  } else {
    if (diffY >= 0) {
      console.log('down swipe');
    } else {
      console.log('up swipe');
    }
  }
}