jquery method to realize photo album sliding twice_jquery

var t1=null; //定义为全局变量

$('body').on('touchstart', '#gallerySlider img', function(e){
var touch = e.originalEvent,
startX = touch.changedTouches[0].pageX;
if (t1 == null){
    t1 = new Date().getTime();
}else{    
    var t2 = new Date().getTime();
    if(t2 - t1 < 500){
      t1 = t2;
      return;
    }else{
      t1 = t2;
    }
}

slider.on('touchmove',function(e){
event.stopPropagation();
touch = e.originalEvent.touches[0] ||
e.originalEvent.changedTouches[0];

if(touch.pageX - startX > 10){
slider.off('touchmove');
showPrevious();
}
else if (touch.pageX - startX < -10){
slider.off('touchmove');
showNext();
}
});
return false;
}).on('touchend',function(){
slider.off('touchmove');
});