jquery 判断手势滑动方向（上下左右）

$('body').on('click', '.placeholder img', function(e) {
    //touchstart在你之前发生，不管些什么，都先执行下面的
});
 
$('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');
        });