Staggered Word Reveal

<h1 class="word-reveal" data-word-reveal>
  Build interfaces that feel calm, cinematic, and alive.
</h1>

.word-reveal {
  visibility: visible;
}

html.js .word-reveal[data-word-reveal]:not(.is-ready) {
  opacity: 0;
}

.word-reveal__word {
  display: inline-block;
  opacity: 0;
  transform: translate3d(0, 20px, 0);
  transition:
    opacity 0.8s cubic-bezier(0.16, 1, 0.3, 1),
    transform 0.8s cubic-bezier(0.16, 1, 0.3, 1);
  transition-delay: calc(var(--word-index) * 0.07s);
  will-change: opacity, transform;
}

.word-reveal.is-visible .word-reveal__word {
  opacity: 1;
  transform: translate3d(0, 0, 0);
}

@media (prefers-reduced-motion: reduce) {
  html.js .word-reveal[data-word-reveal]:not(.is-ready),
  .word-reveal__word {
    opacity: 1;
    transform: none;
    transition: none;
  }
}

document.documentElement.classList.add("js");

function splitWordReveal(element) {
  if (element.dataset.wordRevealReady === "true") return;

  const text = element.textContent || "";
  const parts = text.split(/(\s+)/);
  let wordIndex = 0;

  element.textContent = "";
  element.setAttribute("aria-label", text.trim());

  parts.forEach((part) => {
    if (!part.trim()) {
      element.appendChild(document.createTextNode(part));
      return;
    }

    const word = document.createElement("span");
    word.className = "word-reveal__word";
    word.setAttribute("aria-hidden", "true");
    word.style.setProperty("--word-index", wordIndex);
    word.textContent = part;

    element.appendChild(word);
    wordIndex += 1;
  });

  element.dataset.wordRevealReady = "true";
  element.classList.add("is-ready");
}

function initWordReveals(selector = "[data-word-reveal]") {
  const elements = Array.from(document.querySelectorAll(selector));
  const reduceMotion = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

  if (reduceMotion || !("IntersectionObserver" in window)) {
    elements.forEach((element) => {
      element.classList.add("is-ready", "is-visible");
    });
    return;
  }

  const observer = new IntersectionObserver(
    (entries, io) => {
      entries.forEach((entry) => {
        if (!entry.isIntersecting) return;

        entry.target.classList.add("is-visible");
        io.unobserve(entry.target);
      });
    },
    {
      threshold: 0.2,
      rootMargin: "0px 0px -10% 0px",
    }
  );

  elements.forEach((element) => {
    splitWordReveal(element);
    observer.observe(element);
  });
}

document.addEventListener("DOMContentLoaded", () => {
  initWordReveals();
});