$('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');

        });