Letter Slam

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Letter Slam: letters drop from huge to normal size one at a time, as if
    // falling towards the page, and each one lands with a jolt that shakes
    // the whole line.
    // Usage: <h1 data-letter-slam>SLAM</h1>
    // Optional: data-loop (letters fade off and slam in again), data-hold (ms
    // to stay before fading), data-scale (how big letters start; default 3.2),
    // data-shake (how hard each landing jolts the line, in px; default 6, 0
    // for none), data-duration (ms for each letter's fall), data-stagger (ms
    // between letters), data-delay (ms before starting).
    var DEFAULTS = { scale: 3.2, shake: 6, duration: 360, stagger: 120, delay: 0, hold: 1600 };

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

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

    // The letters go inside one inner span, so the jolt can shake them all
    // without touching the element's own transform.
    function split(el) {
      var text = el.textContent.replace(/\s+/g, ' ').trim();
      el.setAttribute('aria-label', text);
      el.textContent = '';
      var inner = document.createElement('span');
      inner.className = 'lsl-inner';
      inner.setAttribute('aria-hidden', 'true');
      var chars = [];
      text.split(' ').forEach(function (word, i) {
        if (i) inner.appendChild(document.createTextNode(' '));
        var w = document.createElement('span');
        w.className = 'lsl-word';
        Array.from(word).forEach(function (c) {
          var s = document.createElement('span');
          s.className = 'lsl-char';
          s.textContent = c;
          w.appendChild(s);
          chars.push(s);
        });
        inner.appendChild(w);
      });
      el.appendChild(inner);
      return { inner: inner, chars: chars };
    }

    // A short, decaying shudder. Each landing starts a fresh one, taking over
    // from wherever the last one had got to.
    function jolt(inner, shake, side) {
      anime.animate(inner, {
        y: [
          { to: shake, duration: 45, ease: 'out(2)' },
          { to: -shake * 0.45, duration: 80, ease: 'inOut(2)' },
          { to: shake * 0.2, duration: 80, ease: 'inOut(2)' },
          { to: 0, duration: 120, ease: 'out(2)' }
        ],
        rotate: [
          { to: side * shake * 0.12, duration: 45, ease: 'out(2)' },
          { to: 0, duration: 260, ease: 'out(2)' }
        ]
      });
    }

    function play(el) {
      var st = el._lsl;
      var d = el.dataset;
      var loop = d.loop !== undefined && d.loop !== 'false';
      var duration = +d.duration || DEFAULTS.duration;
      var stagger = +d.stagger || DEFAULTS.stagger;
      var scale = +d.scale || DEFAULTS.scale;
      var shake = d.shake !== undefined ? +d.shake : DEFAULTS.shake;

      var tl = anime.createTimeline({ loop: loop, loopDelay: 400, delay: +d.delay || DEFAULTS.delay });
      st.chars.forEach(function (c, i) {
        var at = i * stagger;
        // Speeding up as it falls, so it hits rather than glides.
        tl.add(c, {
          scale: { from: scale, to: 1, ease: 'in(3)' },
          opacity: { from: 0, to: 1, duration: duration * 0.6, ease: 'out(2)' },
          duration: duration
        }, at);
        if (shake) tl.call(function () { jolt(st.inner, shake, i % 2 ? 1 : -1); }, at + duration);
      });
      if (loop) {
        tl.add(st.chars, {
          opacity: 0,
          scale: 0.85,
          duration: 500,
          ease: 'in(2)',
          delay: anime.stagger(30)
        }, '+=' + (+d.hold || DEFAULTS.hold));
      }
    }

    function init() {
      var io = new IntersectionObserver(function (entries) {
        entries.forEach(function (e) {
          if (!e.isIntersecting) return;
          io.unobserve(e.target);
          play(e.target);
        });
      }, { threshold: 0.2 });
      document.querySelectorAll('[data-letter-slam]').forEach(function (el) {
        if (el._lsl) return;
        el._lsl = split(el);
        if (reduced()) return;
        anime.utils.set(el._lsl.chars, { opacity: 0 });
        io.observe(el);
      });
    }

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

<h1 data-letter-slam>Hit hard</h1>

<!-- a gentler landing: -->
<h1 data-letter-slam data-scale="2" data-shake="3">Hit hard</h1>