javascript 移动端判断用户是上滑还是下滑页面

var startX, startY;
document.addEventListener('touchstart', function(ev) {
    startX = ev.touches[0].pageX;
    startY = ev.touches[0].pageY;
}, false);

document.addEventListener('touchmove', function(ev) {
    var endX, endY;
    endX = ev.changedTouches[0].pageX;
    endY = ev.changedTouches[0].pageY;
    var direction = GetSlideDirection(startX, startY, endX, endY);
    switch (direction) {
        case 0:
            console.log("无操作");
            break;
        case 1:
            // 向上
            console.log("向上");
            break;
        case 2:
            // 向下
            console.log("向下");
            break;
    }
}, false);

function GetSlideDirection(startX, startY, endX, endY) {
    var dy = startY - endY;
    var result = 0;
    if (dy > 0) { 
        //向上滑动
        result = 1;
    } else if (dy < 0) { 
        //向下滑动
        result = 2;
    } else {
        result = 0;
    }
    return result;
}