Curtain Wipe

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Curtain Wipe: a page transition. A coloured curtain sweeps up to cover the
    // page when a link is clicked, and lifts away again when the next page opens.
    // Usage: <body data-curtain-wipe>   (add the snippet to every page)
    // Optional: data-curtain-wipe="#6a0dad" (curtain colour), data-duration (ms).
    // Contained mode: put data-curtain-wipe on any other element with two or
    // more children and it wipes between them every data-interval ms (a slideshow).
    var DEFAULTS = { color: '#6a0dad', duration: 650, interval: 2400 };

    var css =
      '.cw-panel{position:fixed;inset:0;z-index:2147483000;pointer-events:none;transform:scaleY(0)}' +
      '.cw-contained{position:relative;overflow:hidden;display:grid}' +
      '.cw-contained>*:not(.cw-panel){grid-area:1/1}' +
      '.cw-contained>.cw-panel{position:absolute}';
    var style = document.createElement('style');
    style.textContent = css;
    document.head.appendChild(style);

    function panel(parent, color) {
      var p = document.createElement('div');
      p.className = 'cw-panel';
      p.setAttribute('aria-hidden', 'true');
      p.style.background = color;
      parent.appendChild(p);
      return p;
    }

    // Cover: grows up from the bottom. Reveal: shrinks away upwards.
    function cover(p, duration, done) {
      anime.utils.set(p, { transformOrigin: '50% 100%' });
      anime.animate(p, { scaleY: [0, 1], duration: duration, ease: 'inOut(3)', onComplete: done });
    }
    function reveal(p, duration, done) {
      anime.utils.set(p, { transformOrigin: '50% 0%' });
      anime.animate(p, { scaleY: [1, 0], duration: duration, ease: 'inOut(3)', onComplete: done });
    }

    function pageMode(body) {
      var color = body.getAttribute('data-curtain-wipe') || DEFAULTS.color;
      var duration = +body.dataset.duration || DEFAULTS.duration;
      var p = panel(body, color);
      anime.utils.set(p, { scaleY: 1 });
      reveal(p, duration);

      document.addEventListener('click', function (e) {
        var a = e.target.closest && e.target.closest('a[href]');
        if (!a || e.defaultPrevented || e.button !== 0 || e.metaKey || e.ctrlKey || e.shiftKey || e.altKey) return;
        if (a.target && a.target !== '_self') return;
        if (a.hasAttribute('download')) return;
        var url = new URL(a.href, location.href);
        if (url.origin !== location.origin) return;
        // Same page, only the #hash changes: let the browser scroll.
        if (url.pathname === location.pathname && url.search === location.search && url.hash) return;
        e.preventDefault();
        cover(p, duration, function () { location.href = url.href; });
      });
      // Coming back with the Back button can restore the covered page: lift it.
      window.addEventListener('pageshow', function (e) {
        if (e.persisted) anime.utils.set(p, { scaleY: 0 });
      });
    }

    function containedMode(el) {
      el.classList.add('cw-contained');
      var slides = Array.from(el.children);
      var color = el.getAttribute('data-curtain-wipe') || DEFAULTS.color;
      var duration = +el.dataset.duration || DEFAULTS.duration;
      var p = panel(el, color);
      var i = 0;
      slides.forEach(function (s, n) { s.style.visibility = n ? 'hidden' : 'visible'; });
      setInterval(function () {
        cover(p, duration, function () {
          slides[i].style.visibility = 'hidden';
          i = (i + 1) % slides.length;
          slides[i].style.visibility = 'visible';
          reveal(p, duration);
        });
      }, (+el.dataset.interval || DEFAULTS.interval) + duration * 2);
    }

    function init() {
      if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) return;
      document.querySelectorAll('[data-curtain-wipe]').forEach(function (el) {
        if (el._cw) return;
        el._cw = true;
        if (el === document.body) pageMode(el);
        else if (el.children.length > 1) containedMode(el);
      });
    }

    if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', init);
    else init();
  })();
</script>

<body data-curtain-wipe="#6a0dad">
  …
</body>