Slit In

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Slit In: the element opens out of a thin slit in 3D. It starts far
    // back and edge-on, rushes forward still almost edge-on, then swings
    // open to face you.
    // Usage: <div data-slit-in>…</div>
    // Optional: data-axis ("y", default, a vertical slit that opens
    // sideways; "x" a horizontal slit that opens up and down; give both,
    // "y x", and each loop uses the next), data-depth (how far back it
    // starts, in px, default 600), data-perspective (px, default 800),
    // data-duration (ms, default 900), data-delay (ms before the first
    // entrance), data-loop (hold, fade away and open again), data-hold (ms to
    // stay when looping, default 1400).
    var DEFAULTS = { axis: 'y', depth: 600, perspective: 800, duration: 900, delay: 0, hold: 1400 };

    function reduced() {
      return window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    }

    function enter(el, axis, done) {
      var d = el.dataset;
      var t = +d.duration || DEFAULTS.duration;
      var depth = +d.depth || DEFAULTS.depth;
      var prop = axis === 'x' ? 'rotateX' : 'rotateY';
      var other = axis === 'x' ? 'rotateY' : 'rotateX';
      var start = { opacity: 0, perspective: (+d.perspective || DEFAULTS.perspective) + 'px', z: -depth };
      start[prop] = 90;
      start[other] = 0;
      anime.utils.set(el, start);
      var props = {
        opacity: { to: 1, duration: t * 0.45, ease: 'linear' },
        // Rush forward while still a slit, then swing open the rest of the way.
        z: [
          { to: -depth * 0.25, duration: t * 0.5, ease: 'out(2)' },
          { to: 0, duration: t * 0.5, ease: 'out(3)' }
        ],
        onComplete: done
      };
      props[prop] = [
        { to: 84, duration: t * 0.5, ease: 'out(2)' },
        { to: 0, duration: t * 0.5, ease: 'out(3)' }
      ];
      anime.animate(el, props);
    }

    function cycle(el) {
      var d = el.dataset;
      var s = el._slt;
      var axes = (d.axis || DEFAULTS.axis).split(/[\s,]+/);
      enter(el, axes[s.n++ % axes.length], function () {
        if (d.loop === undefined || d.loop === 'false') return;
        setTimeout(function () {
          anime.animate(el, {
            opacity: 0,
            duration: 400,
            ease: 'out(2)',
            onComplete: function () {
              // Wait until it's back on screen before the next entrance.
              setTimeout(function () {
                if (s.visible) cycle(el);
                else s.waiting = true;
              }, 500);
            }
          });
        }, +d.hold || DEFAULTS.hold);
      });
    }

    function init() {
      var io = new IntersectionObserver(function (entries) {
        entries.forEach(function (e) {
          var s = e.target._slt;
          s.visible = e.isIntersecting;
          if (!e.isIntersecting) return;
          if (!s.started) {
            s.started = true;
            setTimeout(function () { cycle(e.target); }, +e.target.dataset.delay || DEFAULTS.delay);
          } else if (s.waiting) {
            s.waiting = false;
            cycle(e.target);
          }
        });
      }, { threshold: 0.2 });
      document.querySelectorAll('[data-slit-in]').forEach(function (el) {
        if (el._slt) return;
        el._slt = { n: 0 };
        if (reduced()) return;
        anime.utils.set(el, { opacity: 0 });
        io.observe(el);
      });
    }

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

<div class="card" data-slit-in>Door unlocked</div>

<!-- or a horizontal slit: -->
<div class="card" data-slit-in data-axis="x">Door unlocked</div>