判断touchmove上下的方向

var a = 0;
$(window).on('touchstart' , function(e){
    a = e.touches[0].screenY;
});
$(window).on('touchmove' , function(e){
    var disY = e.touches[0].screenY - a;
        if(disY > 0){
          alert('向下')  
        }else{
           alert('向上')
        }
}