Long Shadow Reveal

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Long Shadow Reveal: the letters pop up, then a long, flat shadow grows
    // out of them at an angle.
    // Usage: <h1 data-long-shadow-reveal>Long shadow</h1>
    // Optional: data-color (the shadow, default "#4c1d95"; use a solid colour a
    // little darker than the background), data-length (in em, default 0.6),
    // data-angle (degrees, 45 = down-right, default 45), data-duration (ms for
    // the shadow to grow, default 1000), data-stagger (ms between letters,
    // default 40), data-loop (shadow shrinks, letters drop, and again),
    // data-hold (ms to stay, when looping), data-delay (ms before starting).
    var DEFAULTS = { color: '#4c1d95', length: 0.6, angle: 45, duration: 1000, stagger: 40, hold: 1800, delay: 0 };

    var css =
      '.lshr-word{display:inline-block;white-space:nowrap}' +
      '.lshr-ch{display:inline-block;will-change:transform}';
    var style = document.createElement('style');
    style.textContent = css;
    document.head.appendChild(style);

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

    function split(el) {
      var text = el.textContent.replace(/\s+/g, ' ').trim();
      el.setAttribute('aria-label', text);
      el.textContent = '';
      var chars = [];
      text.split(' ').forEach(function (word, i) {
        if (i) el.appendChild(document.createTextNode(' '));
        var w = document.createElement('span');
        w.className = 'lshr-word';
        w.setAttribute('aria-hidden', 'true');
        Array.from(word).forEach(function (c) {
          var s = document.createElement('span');
          s.className = 'lshr-ch';
          s.textContent = c;
          w.appendChild(s);
          chars.push(s);
        });
        el.appendChild(w);
      });
      return chars;
    }

    // A stack of 1px-apart shadows, `k` (0 to 1) of the full length.
    function shadow(el, k) {
      var d = el.dataset;
      var fs = parseFloat(getComputedStyle(el).fontSize);
      var len = Math.round(fs * (+d.length || DEFAULTS.length) * k);
      var a = (d.angle !== undefined ? +d.angle : DEFAULTS.angle) * Math.PI / 180;
      var dx = Math.cos(a), dy = Math.sin(a), color = d.color || DEFAULTS.color;
      var parts = [];
      for (var i = 1; i <= len; i++) {
        parts.push((dx * i).toFixed(1) + 'px ' + (dy * i).toFixed(1) + 'px 0 ' + color);
      }
      el.style.textShadow = parts.length ? parts.join(',') : 'none';
    }

    function play(el) {
      var d = el.dataset, s = el._lshr;
      var loop = d.loop !== undefined && d.loop !== 'false';
      var duration = +d.duration || DEFAULTS.duration;
      var stagger = d.stagger !== undefined ? +d.stagger : DEFAULTS.stagger;
      var g = { k: 0 };
      var tl = anime.createTimeline({
        onComplete: function () { if (loop) setTimeout(function () { play(el); }, 300); }
      });
      tl.add(s.chars, {
        opacity: [0, 1],
        y: ['0.5em', '0em'],
        scale: [0.3, 1],
        duration: 650,
        ease: 'outBack(2)',
        delay: anime.stagger(stagger)
      });
      tl.add(g, {
        k: [0, 1],
        duration: duration,
        ease: 'outQuart',
        onUpdate: function () { shadow(el, g.k); }
      }, '-=250');
      if (loop) {
        tl.add(g, {
          k: [1, 0],
          duration: duration * 0.5,
          ease: 'inQuad',
          onUpdate: function () { shadow(el, g.k); }
        }, '+=' + (+d.hold || DEFAULTS.hold));
        tl.add(s.chars, {
          opacity: [1, 0],
          y: ['0em', '0.3em'],
          scale: [1, 0.6],
          duration: 350,
          ease: 'inQuad',
          delay: anime.stagger(stagger * 0.5)
        });
      }
    }

    function init() {
      var io = new IntersectionObserver(function (entries) {
        entries.forEach(function (e) {
          if (!e.isIntersecting) return;
          io.unobserve(e.target);
          var el = e.target;
          setTimeout(function () { play(el); }, +el.dataset.delay || DEFAULTS.delay);
        });
      }, { threshold: 0.2 });
      document.querySelectorAll('[data-long-shadow-reveal]').forEach(function (el) {
        if (el._lshr) return;
        el._lshr = { chars: split(el) };
        if (reduced()) { shadow(el, 1); return; }
        el._lshr.chars.forEach(function (c) { c.style.opacity = 0; });
        io.observe(el);
      });
    }

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

<h1 data-long-shadow-reveal data-color="#4c1d95">Long shadow</h1>

<!-- or, a longer shadow falling down-left: -->
<h1 data-long-shadow-reveal data-length="1" data-angle="135">Long shadow</h1>