Js判断页面滚动方向

const detectScrollDirection = () => {
  let lastScrollTop = 0;
  window.addEventListener("scroll", () => {
    const header = document.querySelector(".site_nav");
    const currentScrollTop =
      document.body.scrollTop || document.documentElement.scrollTop;
    if (currentScrollTop < lastScrollTop) { //<向下滚动，>向上滚动
      header.classList.remove("scroll");
    } else {
      header.classList.add("scroll");
    }
    lastScrollTop = currentScrollTop;
  });
};
detectScrollDirection();