Row Collapse

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Row Collapse: a removed list item slides aside and fades, then its row
    // folds shut so the items around it glide together to close the gap.
    // Usage: <li data-row-collapse>…</li>
    // It plays once the item has been in view for data-delay ms. Without
    // data-loop it ends hidden (display: none), so call
    // animacious.rowCollapse(el, done) and remove it in done if you like.
    // Optional: data-to (the way it slides as it fades: "right", default,
    // "left", or "none" to shrink in place), data-duration (ms, default 700),
    // data-delay (ms in view before it goes, default 1200), data-loop (open
    // the gap again, fade back in, hold and collapse again), data-hold (ms to
    // stay between removals when looping, default 1400).
    // Script use: animacious.rowCollapse(el, done) plays it on any element
    // now, using its data-* options, and calls done afterwards.
    var DEFAULTS = { to: 'right', duration: 700, delay: 1200, hold: 1400 };
    var BOX = ['height', 'paddingTop', 'paddingBottom', 'marginTop', 'marginBottom', 'borderTopWidth', 'borderBottomWidth'];

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

    // Hold the row at its current size so those sizes can be animated.
    function freeze(el) {
      var cs = getComputedStyle(el);
      var box = {};
      BOX.forEach(function (k) { box[k] = cs[k]; });
      el._rwcBox = box;
      BOX.forEach(function (k) { el.style[k] = box[k]; });
      el.style.minHeight = '0px';
      el.style.overflow = 'hidden';
      return box;
    }

    function unfreeze(el) {
      BOX.concat(['minHeight', 'overflow']).forEach(function (k) { el.style[k] = ''; });
    }

    function leave(el, done) {
      var d = el.dataset;
      var t = +d.duration || DEFAULTS.duration;
      var to = d.to || DEFAULTS.to;
      if (reduced()) {
        el.style.display = 'none';
        if (done) done();
        return;
      }
      anime.utils.set(el, { x: 0, scale: 1, opacity: 1 });
      var slide = to === 'none' ? 0 : Math.min(60, el.offsetWidth * 0.15) * (to === 'left' ? -1 : 1);
      freeze(el);
      var shut = {};
      BOX.forEach(function (k) { shut[k] = '0px'; });
      shut.duration = t * 0.55;
      shut.ease = 'inOut(3)';
      anime.createTimeline({
        onComplete: function () {
          if (done) done();
        }
      })
        // The item shrinks and slides aside…
        .add(el, {
          x: { to: slide, ease: 'in(2)' },
          scale: { to: to === 'none' ? 0.85 : 0.94, ease: 'in(2)' },
          opacity: { to: 0, ease: 'in(1.5)' },
          duration: t * 0.45
        })
        // …then the gap it leaves closes up.
        .add(el, shut);
    }

    function back(el, done) {
      var box = el._rwcBox;
      var open = {};
      BOX.forEach(function (k) { open[k] = box[k]; });
      open.duration = 450;
      open.ease = 'inOut(3)';
      anime.utils.set(el, { x: 0, scale: 0.94 });
      open.onComplete = function () {
        unfreeze(el);
        anime.animate(el, { opacity: 1, scale: 1, duration: 400, ease: 'out(2)', onComplete: done });
      };
      anime.animate(el, open);
    }

    function cycle(el) {
      var d = el.dataset;
      var s = el._rwc;
      leave(el, function () {
        if (d.loop === undefined || d.loop === 'false') {
          unfreeze(el);
          el.style.display = 'none';
          return;
        }
        // Open the gap again, then go again once it's on screen.
        setTimeout(function () {
          back(el, function () {
            setTimeout(function () {
              if (s.visible) cycle(el);
              else s.waiting = true;
            }, +d.hold || DEFAULTS.hold);
          });
        }, 700);
      });
    }

    window.animacious = window.animacious || {};
    window.animacious.rowCollapse = function (el, done) {
      leave(el, function () {
        unfreeze(el);
        el.style.display = 'none';
        if (done) done(el);
      });
    };

    function init() {
      var io = new IntersectionObserver(function (entries) {
        entries.forEach(function (e) {
          var s = e.target._rwc;
          s.visible = e.isIntersecting;
          if (!e.isIntersecting) return;
          if (!s.started) {
            s.started = true;
            var wait = e.target.dataset.delay;
            setTimeout(function () { cycle(e.target); }, wait === undefined ? DEFAULTS.delay : +wait || 0);
          } else if (s.waiting) {
            s.waiting = false;
            cycle(e.target);
          }
        });
      }, { threshold: 0.2 });
      document.querySelectorAll('[data-row-collapse]').forEach(function (el) {
        if (el._rwc) return;
        el._rwc = {};
        if (!reduced()) io.observe(el);
      });
    }

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

<ul class="inbox">
  <li>Lunch on Friday?</li>
  <li data-row-collapse>48 hours only: 30% off</li>
  <li>Here are the photos</li>
</ul>

<!-- or on demand, when a delete button is clicked: -->
<script>
  button.addEventListener('click', function () {
    animacious.rowCollapse(item, function () { item.remove(); });
  });
</script>