[!]


let old_scroll_top = document.documentElement.scrollTop;

function onscroll() {
    if (document.documentElement.scrollTop > old_scroll_top + 100) {
        document.getElementById("header").classList.add("hide");
        old_scroll_top = document.documentElement.scrollTop;
    }
    if (document.documentElement.scrollTop < old_scroll_top) {
        old_scroll_top = document.documentElement.scrollTop;
        document.getElementById("header").classList.remove("hide");
    }
}

window.addEventListener("wheel", onscroll);
window.addEventListener("scroll", onscroll);