Jack-in-the-box

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Jack-in-the-box: the element springs up from a squashed state at its
    // base, overshoots, and wobbles side to side before it settles upright.
    // Usage: <div data-jack-in-the-box>…</div>
    // Optional: data-wobble (how far it rocks, in degrees, default 12),
    // data-duration (ms, default 1200), data-delay (ms before the first
    // entrance), data-loop (hold, fade away and spring up again), data-hold
    // (ms to stay when looping, default 1400).
    var DEFAULTS = { wobble: 12, duration: 1200, delay: 0, hold: 1400 };

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

    function enter(el, done) {
      var d = el.dataset;
      var t = +d.duration || DEFAULTS.duration;
      var w = d.wobble === undefined ? DEFAULTS.wobble : +d.wobble || 0;
      // It springs from its base, like a toy out of its box.
      el.style.transformOrigin = '50% 100%';
      anime.utils.set(el, { scaleX: 0.6, scaleY: 0.05, rotate: 0, opacity: 0 });
      anime.createTimeline({ onComplete: done })
        .add(el, { opacity: { to: 1, duration: t * 0.12, ease: 'linear' } }, 0)
        // Shoot up past full height, then spring back to it.
        .add(el, {
          scaleY: [
            { to: 1.18, duration: t * 0.22, ease: 'out(3)' },
            { to: 0.92, duration: t * 0.16, ease: 'inOut(2)' },
            { to: 1.04, duration: t * 0.14, ease: 'inOut(2)' },
            { to: 1, duration: t * 0.18, ease: 'out(2)' }
          ],
          scaleX: [
            { to: 0.9, duration: t * 0.22, ease: 'out(3)' },
            { to: 1.06, duration: t * 0.16, ease: 'inOut(2)' },
            { to: 0.98, duration: t * 0.14, ease: 'inOut(2)' },
            { to: 1, duration: t * 0.18, ease: 'out(2)' }
          ]
        }, 0)
        // Rock side to side on its base, each swing smaller.
        .add(el, {
          rotate: [
            { to: -w, duration: t * 0.2, ease: 'out(2)' },
            { to: w * 0.6, duration: t * 0.2, ease: 'inOut(2)' },
            { to: -w * 0.3, duration: t * 0.18, ease: 'inOut(2)' },
            { to: w * 0.1, duration: t * 0.16, ease: 'inOut(2)' },
            { to: 0, duration: t * 0.14, ease: 'out(2)' }
          ]
        }, t * 0.12);
    }

    function cycle(el) {
      var d = el.dataset;
      var s = el._jib;
      enter(el, 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._jib;
          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-jack-in-the-box]').forEach(function (el) {
        if (el._jib) return;
        el._jib = {};
        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-jack-in-the-box>Surprise!</div>

<!-- or a calmer spring with less rocking: -->
<div class="card" data-jack-in-the-box data-wobble="5">Surprise!</div>