Zoom Through Rotator

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/bundles/anime.umd.min.js"></script>
<script>
  (function () {
    // Zoom Through Rotator: the word in your sentence rushes towards you,
    // growing and blurring until it vanishes, as the next word zooms in from
    // far away and settles into place.
    // Usage: <h1>Go <span data-zoom-through-rotator="further, faster, beyond">further</span></h1>
    // Optional: data-hold (ms per word, default 1800), data-duration (ms per
    // swap, default 800), data-scale (how big the old word grows as it flies
    // past, default 1.8), data-blur (px, default 6).
    var DEFAULTS = { hold: 1800, duration: 800, scale: 1.8, blur: 6 };

    var css =
      '.ztr{display:inline-block;position:relative;white-space:nowrap;vertical-align:baseline;text-align:left}' +
      '.ztr-word{display:inline-block;white-space:nowrap;will-change:transform,opacity,filter}' +
      '.ztr-old{position:absolute;left:0;top:0;pointer-events:none}' +
      '.ztr-probe{position:absolute;left:0;top:0;visibility:hidden;white-space:nowrap}' +
      '.ztr-sr{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}';
    var style = document.createElement('style');
    style.textContent = css;
    document.head.appendChild(style);

    function span(cls, parent, text) {
      var s = document.createElement('span');
      s.className = cls;
      if (text) s.textContent = text;
      parent.appendChild(s);
      return s;
    }

    function setup(el) {
      var words = (el.getAttribute('data-zoom-through-rotator') || el.textContent)
        .split(',').map(function (w) { return w.trim(); }).filter(Boolean);
      el.classList.add('ztr');
      el.textContent = '';
      span('ztr-sr', el, words.join(', '));
      var out = span('ztr-word', el, words[0]);
      var probe = span('ztr-probe', el);
      out.setAttribute('aria-hidden', 'true');
      probe.setAttribute('aria-hidden', 'true');
      return { el: el, words: words, out: out, probe: probe, i: 0, w: 0, busy: false, visible: false, started: false };
    }

    function measure(s, text) {
      s.probe.textContent = text;
      return s.probe.offsetWidth;
    }

    function fit(s) {
      if (s.busy) return;
      s.w = measure(s, s.words[s.i]);
      s.el.style.width = s.w + 'px';
    }

    function swap(s, done) {
      var d = s.el.dataset;
      var t = +d.duration || DEFAULTS.duration;
      var big = +d.scale || DEFAULTS.scale;
      var blur = (d.blur !== undefined ? +d.blur : DEFAULTS.blur) + 'px';
      s.i = (s.i + 1) % s.words.length;
      var to = s.words[s.i];
      s.busy = true;

      // The old word flies at the viewer: it grows, blurs and fades out fast.
      var old = s.out;
      old.classList.add('ztr-old');
      anime.animate(old, {
        scale: [1, big], opacity: [1, 0], filter: ['blur(0px)', 'blur(' + blur + ')'],
        duration: t * 0.55, ease: 'in(2)',
        onComplete: function () { old.remove(); }
      });

      // The new word starts tiny and far away, then rushes into focus.
      s.out = span('ztr-word', s.el, to);
      s.out.setAttribute('aria-hidden', 'true');
      s.el.insertBefore(s.out, s.probe);
      anime.utils.set(s.out, { opacity: 0, scale: 0.25 });
      anime.animate(s.out, {
        scale: [0.25, 1], opacity: [0, 1], filter: ['blur(' + blur + ')', 'blur(0px)'],
        duration: t * 0.75, delay: t * 0.25, ease: 'out(4)'
      });

      anime.animate(s, {
        w: measure(s, to), duration: t, ease: 'inOut(3)',
        onUpdate: function () { s.el.style.width = s.w.toFixed(2) + 'px'; },
        onComplete: function () { s.busy = false; done(); }
      });
    }

    // Wait, then run fn, but only once the word is on screen.
    function wait(s, ms, fn) {
      setTimeout(function check() {
        if (s.visible && !document.hidden) fn();
        else setTimeout(check, 300);
      }, ms);
    }

    function start(s) {
      fit(s);
      if (document.fonts) document.fonts.ready.then(function () { fit(s); });
      window.addEventListener('resize', function () { fit(s); });
      var hold = +s.el.dataset.hold || DEFAULTS.hold;
      (function loop() {
        wait(s, hold, function () { swap(s, loop); });
      })();
    }

    function init() {
      var reduced = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
      var io = new IntersectionObserver(function (entries) {
        entries.forEach(function (e) {
          var s = e.target._ztr;
          s.visible = e.isIntersecting;
          if (s.visible && !s.started) { s.started = true; start(s); }
        });
      }, { threshold: 0.3 });
      document.querySelectorAll('[data-zoom-through-rotator]').forEach(function (el) {
        if (el._ztr) return;
        el._ztr = setup(el);
        if (!reduced && el._ztr.words.length > 1) io.observe(el);
      });
    }

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

<h1>
  Go
  <span data-zoom-through-rotator="further, faster, beyond">further</span>
</h1>