H5 中监听页面滚动事件，判断滚动方向的方法

//监听页面滚动事件
function scrollEvent() {
window.onscroll = function(e){
scrollFunc();
if(scrollDirection == 'down'){
//页面向下滚动要做的事情
}
else if(scrollDirection == 'up'){
//页面向上滚动要做的事情
}
}
}

var scrollAction = {x: 'undefined', y: 'undefined'}, scrollDirection;
function scrollFunc() {
if (typeof scrollAction.x == 'undefined') {
scrollAction.x = window.pageXOffset;
scrollAction.y = window.pageYOffset;
}
var diffX = scrollAction.x - window.pageXOffset;
var diffY = scrollAction.y - window.pageYOffset;
if (diffX < 0) {
// Scroll right
scrollDirection = 'right';
} else if (diffX > 0) {
// Scroll left
scrollDirection = 'left';
} else if (diffY < 0) {
// Scroll down
scrollDirection = 'down';
} else if (diffY > 0) {
// Scroll up
scrollDirection = 'up';
} else {
// First scroll event
}
scrollAction.x = window.pageXOffset;
scrollAction.y = window.pageYOffset;
}