如何确定jQuery滚动事件的方向？

var prevScrollPos = 0;

$(window).scroll(function() {
  var currentScrollPos = $(window).scrollTop();
  var scrollDirection = currentScrollPos - prevScrollPos;

  if (scrollDirection > 0) {
    console.log("向下滚动");
  } else if (scrollDirection < 0) {
    console.log("向上滚动");
  } else {
    console.log("没有滚动");
  }

  prevScrollPos = currentScrollPos;
});