var lastTouchTime = 0;
var lastTouchPos = null;

document.body.addEventListener('touchstart', function(e) {
  var touchPos = e.changedTouches[0];
  var touchTime = e.timeStamp;

  if (touchTime - lastTouchTime < 500 &&
    Math.abs(touchPos.clientX - lastTouchPos.clientX) <= 20 &&
    Math.abs(touchPos.clientY - lastTouchPos.clientY) <= 20) {
    lastTouchTime = 0;
    
    /* DO SOMETHING HERE... */
  } else {
    lastTouchTime = touchTime;
  }

  lastTouchPos = touchPos;
});