code: function gestureStart(element, clientX, clientY) {
    element[startXKey] = clientX;
    element[startYKey] = clientY;
    element[previousXKey] = clientX;
    element[previousYKey] = clientY;
    element[previousTimeKey] = Date.now();
    element[previousVelocityKey] = 0;
    element.setState({ swipeFraction: 0 });
  }
docs: /*
  Invoked when the user has begun a touch operation.