var lastKnownScrollY = 0;
var currentScrollY = 0;
var ticking = false;
var idOfHeader = 'header';
var eleHeader = null;
const classes = {
pinned: 'header-pin',
unpinned: 'header-unpin',
};
function onScroll() {
currentScrollY = window.pageYOffset;
if (currentScrollY < lastKnownScrollY) {
pin();
} else if (currentScrollY > lastKnownScrollY) {
unpin();
}
lastKnownScrollY = currentScrollY;
}
function pin() {
if (eleHeader.classList.contains(classes.unpinned)) {
eleHeader.classList.remove(classes.unpinned);
eleHeader.classList.add(classes.pinned);
}
}
function unpin() {
if (eleHeader.classList.contains(classes.pinned) || !eleHeader.classList.contains(classes.unpinned)) {
eleHeader.classList.remove(classes.pinned);
eleHeader.classList.add(classes.unpinned);
}
}
window.onload = function() {
eleHeader = document.getElementById(idOfHeader);
document.addEventListener('scroll', onScroll, false);
}
