Glyph Rain Reveal

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Glyph Rain Reveal: a column of random characters falls into each letter's
    // place, slows down as it arrives and leaves the real letter behind.
    // Usage: <h1 data-glyph-rain-reveal>Decoded</h1>
    // Optional: data-color (the falling trail, default "#a855f7"), data-trail
    // (characters in each column, default 5), data-duration (ms for a column to
    // fall, default 1500), data-stagger (ms of random spread between columns,
    // default 900), data-loop (fade away and rain in again), data-hold (ms to
    // stay before fading, when looping), data-delay (ms before starting).
    var DEFAULTS = { color: '#a855f7', trail: 5, duration: 1500, stagger: 900, hold: 1800, delay: 0 };
    var GLYPHS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789#$%&@*+=<>?/';

    var css =
      '.grr-on{clip-path:inset(-1.4em -0.3em -0.3em -0.3em)}' +
      '.grr-word{display:inline-block;white-space:nowrap}' +
      '.grr-ch{display:inline-block;position:relative;transition:color .6s ease}' +
      '.grr-hide{color:transparent!important}' +
      '.grr-col{position:absolute;left:50%;bottom:0;display:flex;flex-direction:column;align-items:center;' +
      'pointer-events:none;will-change:transform;' +
      '-webkit-mask-image:linear-gradient(to bottom,transparent,#000 70%);mask-image:linear-gradient(to bottom,transparent,#000 70%)}' +
      '.grr-col span{display:block;text-align:center}';
    var style = document.createElement('style');
    style.textContent = css;
    document.head.appendChild(style);

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

    function glyph() { return GLYPHS[(Math.random() * GLYPHS.length) | 0]; }

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

    // Builds the falling column for one letter: trail glyphs on top, the head
    // (which becomes the real letter) at the bottom.
    function column(ch, n, color) {
      var col = document.createElement('span');
      col.className = 'grr-col';
      col.setAttribute('aria-hidden', 'true');
      var h = ch.offsetHeight;
      var cells = [];
      for (var i = 0; i <= n; i++) {
        var g = document.createElement('span');
        g.style.height = h + 'px';
        g.style.lineHeight = h + 'px';
        g.textContent = glyph();
        if (i < n) {
          g.style.color = color;
          g.style.opacity = (0.25 + 0.6 * (i + 1) / n).toFixed(2);
        }
        col.appendChild(g);
        cells.push(g);
      }
      ch.appendChild(col);
      return { col: col, cells: cells, h: h, ch: ch, real: ch.firstChild.nodeValue, landed: false };
    }

    function rain(el, done) {
      var s = el._grr, d = el.dataset;
      var n = Math.max(1, +d.trail || DEFAULTS.trail);
      var color = d.color || DEFAULTS.color;
      var duration = +d.duration || DEFAULTS.duration;
      var spread = d.stagger !== undefined ? +d.stagger : DEFAULTS.stagger;
      var left = s.chars.length;
      var cols = s.chars.map(function (ch) {
        ch.classList.add('grr-hide');
        ch.style.opacity = '';
        ch.style.transform = '';
        return column(ch, n, color);
      });

      // Scramble the glyphs while they fall, slower as each column slows.
      var start = performance.now();
      (function flicker() {
        var live = false;
        cols.forEach(function (c) {
          if (c.landed) return;
          live = true;
          c.cells.forEach(function (g, i) {
            var settling = c.p > 0.7 && i === n;
            if (settling) g.textContent = c.real;
            else if (Math.random() < 0.9 - (c.p || 0) * 0.6) g.textContent = glyph();
          });
        });
        if (live) setTimeout(flicker, 60 + (performance.now() - start) / 40);
      })();

      cols.forEach(function (c) {
        c.p = 0;
        var dur = duration * (0.75 + Math.random() * 0.5);
        var from = -(n + 2 + Math.random() * 3) * c.h;
        c.col.style.transform = 'translate(-50%,' + from + 'px)';
        anime.animate(c, {
          p: [0, 1],
          duration: dur,
          delay: Math.random() * spread,
          ease: 'outCubic',
          onUpdate: function () {
            c.col.style.transform = 'translate(-50%,' + (from * (1 - c.p)).toFixed(1) + 'px)';
          },
          onComplete: function () {
            c.landed = true;
            // The real letter takes over from the head, flashing the trail colour.
            c.ch.style.transition = 'none';
            c.ch.style.color = color;
            c.ch.classList.remove('grr-hide');
            c.cells[n].textContent = '';
            void c.ch.offsetWidth;
            c.ch.style.transition = '';
            requestAnimationFrame(function () { c.ch.style.color = ''; });
            anime.animate(c.col, {
              opacity: [1, 0],
              duration: 500,
              ease: 'outQuad',
              onComplete: function () {
                c.col.remove();
                if (--left === 0 && done) done();
              }
            });
          }
        });
      });
    }

    function play(el) {
      var d = el.dataset;
      var loop = d.loop !== undefined && d.loop !== 'false';
      rain(el, function () {
        if (!loop) return;
        setTimeout(function () {
          anime.animate(el._grr.chars, {
            opacity: [1, 0],
            y: ['0em', '0.4em'],
            duration: 500,
            ease: 'inQuad',
            delay: anime.stagger(30),
            onComplete: function () { setTimeout(function () { play(el); }, 300); }
          });
        }, +d.hold || DEFAULTS.hold);
      });
    }

    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-glyph-rain-reveal]').forEach(function (el) {
        if (el._grr) return;
        el._grr = { chars: split(el) };
        if (reduced()) return;
        el._grr.chars.forEach(function (c) { c.classList.add('grr-hide'); });
        io.observe(el);
      });
    }

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

<h1 data-glyph-rain-reveal>Decoded</h1>

<!-- or, with green trails, looping: -->
<h1 data-glyph-rain-reveal data-color="#22c55e" data-loop>Decoded</h1>