纯js 判断手势滑动方向

$('body').on('touchstart', '#gallerySlider img', function(e) {
var touch = e.originalEvent,
startX = touch.changedTouches[0].pageX;
startY = touch.changedTouches[0].pageY;
slider.on('touchmove', function(e) {
e.preventDefault();
touch = e.originalEvent.touches[0] ||
e.originalEvent.changedTouches[0];
if (touch.pageX - startX > 10) {
console.log("右划");
slider.off('touchmove');
showPrevious();
} else if (touch.pageX - startX < -10) {
console.log("左划");
slider.off('touchmove');
showNext();
};
if (touch.pageY - startY > 10) {
console.log("下划");
} else if (touch.pageY - startY < -10) {
console.log("上划");
};
});

        // Return false to prevent image 
        // highlighting on Android
        return false;

    }).on('touchend', function() {
        slider.off('touchmove');
    });