Shape Morph Loader

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Shape Morph Loader: a shape hops and morphs from circle to square to
    // triangle and back, turning and changing colour as it goes, while its
    // shadow shrinks and grows beneath it. Sized with font-size.
    // It morphs while it's on screen.
    // Usage: <div data-shape-morph-loader aria-label="Loading"></div>
    // Optional: data-colors (three colours, one per shape, default
    // #a855f7,#ec4899,#f59e0b), data-speed (ms per morph, default 650),
    // data-hold (ms on each shape, default 300), data-shadow="false" (no shadow).
    var DEFAULTS = { colors: '#a855f7,#ec4899,#f59e0b', speed: 650, hold: 300 };
    var N = 72; // points per outline: corners of the square and triangle land on them exactly

    var css =
      '.sml{display:inline-grid;justify-items:center;gap:0.2em;vertical-align:middle}' +
      '.sml svg{display:block;width:2em;height:2em;overflow:visible;transform-origin:50% 100%}' +
      '.sml path{stroke-width:7;stroke-linejoin:round;transform-origin:50px 50px}' +
      '.sml-shadow{width:1.5em;height:0.2em;border-radius:50%;background:currentColor;opacity:.14}';
    var style = document.createElement('style');
    style.textContent = css;
    document.head.appendChild(style);

    // Every shape is traced the same way (N points round the centre, starting
    // straight up), so one morphs into another point for point.
    function outline(radius) {
      var pts = [];
      for (var i = 0; i < N; i++) {
        var a = -Math.PI / 2 + (i / N) * Math.PI * 2;
        var r = radius(a);
        pts.push((50 + r * Math.cos(a)).toFixed(2) + ' ' + (50 + r * Math.sin(a)).toFixed(2));
      }
      return 'M' + pts.join(' L') + ' Z';
    }

    var SHAPES = [
      outline(function () { return 40; }),
      outline(function (a) { return 35 / Math.max(Math.abs(Math.cos(a)), Math.abs(Math.sin(a))); }),
      // An upright triangle, centred on its middle: 23 from the centre to each edge.
      outline(function (a) {
        var deg = (a * 180) / Math.PI;
        var off = ((((deg - 30) % 120) + 120) % 120) - 60;
        return 23 / Math.cos((off * Math.PI) / 180);
      })
    ];

    function build(el) {
      var d = el.dataset;
      var colors = (d.colors || DEFAULTS.colors).split(',').map(function (c) { return c.trim(); });
      while (colors.length < 3) colors.push(colors[colors.length - 1]);
      el.classList.add('sml');
      if (!el.getAttribute('role')) el.setAttribute('role', 'progressbar');
      if (!el.getAttribute('aria-label')) el.setAttribute('aria-label', 'Loading');
      el.innerHTML = '<svg viewBox="0 0 100 100" aria-hidden="true"><path/></svg>' +
        (d.shadow === 'false' ? '' : '<span class="sml-shadow" aria-hidden="true"></span>');
      var svg = el.firstChild;
      var path = svg.firstChild;
      var shadow = el.querySelector('.sml-shadow');
      path.setAttribute('d', SHAPES[0]);
      path.setAttribute('fill', colors[0]);
      path.setAttribute('stroke', colors[0]);
      if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) return null;

      var speed = +d.speed || DEFAULTS.speed;
      var step = speed + (+d.hold || DEFAULTS.hold);
      // Each hop turns the shape on: the square lands at 180°, the triangle at 360°
      // (both upright), and the circle can land anywhere, so the loop restarts
      // from 0° without a jump.
      var turns = [180, 360, 480];
      var tl = anime.createTimeline({ loop: true, autoplay: false });
      for (var i = 0; i < 3; i++) {
        var next = (i + 1) % 3;
        var at = i * step;
        tl.add(path, { d: SHAPES[next], fill: colors[next], stroke: colors[next], duration: speed, ease: 'inOut(3)' }, at);
        tl.add(path, {
          rotate: turns[i],
          duration: speed,
          ease: 'inOut(2.4)'
        }, at);
        tl.add(svg, {
          translateY: [{ to: '-0.35em', duration: speed * 0.5, ease: 'out(2)' }, { to: '0em', duration: speed * 0.5, ease: 'in(2)' }],
          scaleY: [{ to: 1, duration: speed }, { to: 0.86, duration: step * 0.12, ease: 'out(2)' }, { to: 1, duration: step * 0.2, ease: 'out(2)' }]
        }, at);
        if (shadow) {
          tl.add(shadow, {
            scale: [{ to: 0.55, duration: speed * 0.5, ease: 'out(2)' }, { to: 1, duration: speed * 0.5, ease: 'in(2)' }],
            opacity: [{ to: 0.07, duration: speed * 0.5, ease: 'out(2)' }, { to: 0.14, duration: speed * 0.5, ease: 'in(2)' }]
          }, at);
        }
      }
      return tl;
    }

    function init() {
      document.querySelectorAll('[data-shape-morph-loader]').forEach(function (el) {
        if (el._sml) return;
        el._sml = true;
        var tl = build(el);
        if (!tl) return;
        // Only morph while visible, to save battery.
        new IntersectionObserver(function (entries) {
          entries[0].isIntersecting ? tl.play() : tl.pause();
        }).observe(el);
      });
    }

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

<div data-shape-morph-loader style="font-size: 32px" aria-label="Loading"></div>