mediawiki-skins-Citizen/resources/scripts/header.js

/*
 * Scroll up Header
 * Modified from https://codepen.io/sajjad/pen/vgEZNy
 */

(function() {
    // Hide header on scroll down
    var didScroll,
        lastScrollTop = 0,
        navbarHeight = 0,
        delta = 0,
        header = document.getElementsByTagName('header')[0],
        headerContainer = document.querySelector('.mw-header-container');

    if (headerContainer !== null) {
        navbarHeight = headerContainer.offsetHeight;
    }

    window.addEventListener('scroll', function() {
        didScroll = true;
    });

    function hasScrolled() {
        var st = window.scrollY,
            body,
            html,
            documentHeight;

        if (Math.abs(lastScrollTop - st) <= delta) {
            return;
        }

        if (st > lastScrollTop && st > navbarHeight) {
            // If scrolled down and past the navbar, add class .nav-up.
            // Scroll Down
            header.classList.remove('nav-down');
            header.classList.add('nav-up');
        } else {
            // Scroll Up
            body = document.body;
            html = document.documentElement;
            documentHeight = Math.max(body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight);

            if (st + window.innerHeight < documentHeight) {
                header.classList.remove('nav-up');
                header.classList.add('nav-down');
            }
        }

        lastScrollTop = st;
    }

    setInterval(function() {
        if (didScroll) {
            hasScrolled();
            didScroll = false;
        }
    }, 250);
})();