Swipe Down in Articulate Storyline

var xDown = null;
var yDown = null;
var player = GetPlayer();
player.SetVar("swipeDown",false);
document.addEventListener('touchstart', function(event) {
  xDown = event.touches[0].clientX;
  yDown = event.touches[0].clientY;
}, false);

document.addEventListener('touchmove', function(event) {
  if (!xDown || !yDown) {
    return;
  }

  var xDiff = xDown - event.touches[0].clientX;
  var yDiff = yDown - event.touches[0].clientY;

  if (Math.abs(xDiff) < Math.abs(yDiff)) {
    if (yDiff < 0) {

      // swipe down detected
      // do something here

        player.SetVar("swipeDown",true);
         player.SetVar("swipeDown",false);

    }
    xDown = null;
    yDown = null;
  }
}, false);

document.addEventListener('touchend', function(event) {
  xDown = null;
  yDown = null;
}, false);