Bottom Up Letters

<!--
  Bottom Up Letters - deterministic text splitter.

  Add class="hf-bottom-up-letters" to a plain text element. This script wraps
  each character in a span so your paused GSAP timeline can stagger the reveal.

  Variables. This fragment has no markup of its own, so the declaration rides
  the <style> element below; the runtime collects every element carrying
  data-composition-variables, not just the document root. The script reads each
  value, falls back to the declared default on anything missing or
  unrecognised, and either changes how the text is split or writes a custom
  property the CSS consumes. The timeline recipe below is untouched by them: it
  still tweens opacity and y back to rest, and these decide what a single
  stagger step covers and where rest is travelled from.

    - unit (letter | word, default letter): what each animated span holds.
      letter staggers glyph by glyph; word keeps whole words intact, so a long
      line reads instead of shimmers.
    - direction (up | down, default up): where the spans start. up starts
      below the baseline and rises into place, down starts above and drops.
    - travel (close | standard | far, default standard): how far each span
      starts from rest, from 0.45em through 0.85em to 1.5em.

  On every default the result is identical to the original: one span per
  character, each starting 0.85em below the baseline.
-->

<style
  data-composition-variables='[
  { "id": "unit", "type": "enum", "role": "content", "label": "Split unit", "description": "What each animated span holds. Letter staggers glyph by glyph, word keeps whole words intact.", "default": "letter", "options": [{ "value": "letter", "label": "Letter" }, { "value": "word", "label": "Word" }] },
  { "id": "direction", "type": "enum", "role": "motion", "label": "Direction", "description": "Where each span starts. Up starts below the baseline and rises, down starts above and drops.", "default": "up", "options": [{ "value": "up", "label": "Up" }, { "value": "down", "label": "Down" }] },
  { "id": "travel", "type": "enum", "role": "motion", "label": "Travel", "description": "How far each span starts from its resting position, from 0.45em to 1.5em.", "default": "standard", "options": [{ "value": "close", "label": "Close" }, { "value": "standard", "label": "Standard" }, { "value": "far", "label": "Far" }] }
]'
>
  .hf-bottom-up-letters {
    display: inline-block;
  }
  .hf-bottom-up-letters-char {
    display: inline-block;
    opacity: 0;
    transform: translate3d(
      0,
      calc(var(--hf-letters-travel, 0.85em) * var(--hf-letters-direction, 1)),
      0
    );
    will-change: transform, opacity;
  }
</style>

<script>
  (function () {
    "use strict";

    var vars =
      window.__hyperframes && window.__hyperframes.getVariables
        ? window.__hyperframes.getVariables()
        : {};

    // Unrecognised overrides return to their declared defaults.
    function pick(table, value, fallback) {
      return Object.prototype.hasOwnProperty.call(table, value) ? value : fallback;
    }

    var travels = { close: "0.45em", standard: "0.85em", far: "1.5em" };
    var directions = { up: "1", down: "-1" };
    var units = { letter: true, word: true };

    var travel = travels[pick(travels, vars.travel, "standard")];
    var direction = directions[pick(directions, vars.direction, "up")];
    var unit = pick(units, vars.unit, "letter");

    document.querySelectorAll(".hf-bottom-up-letters").forEach((el) => {
      el.style.setProperty("--hf-letters-travel", travel);
      el.style.setProperty("--hf-letters-direction", direction);
      if (el.dataset.hfLettersReady === "1") return;
      const text = el.textContent || "";
      el.textContent = "";
      const parts = unit === "word" ? text.split(/(\s+)/) : Array.from(text);
      for (const part of parts) {
        if (part === "") continue;
        if (unit === "word" && /^\s+$/.test(part)) {
          el.appendChild(document.createTextNode(part));
          continue;
        }
        const span = document.createElement("span");
        span.className = "hf-bottom-up-letters-char";
        span.textContent = part === " " ? "\u00a0" : part;
        el.appendChild(span);
      }
      el.dataset.hfLettersReady = "1";
    });
  })();
</script>

<!--
  Timeline integration:

  tl.to(".hf-bottom-up-letters-char", {
    opacity: 1,
    y: 0,
    duration: 0.48,
    ease: "back.out(1.7)",
    stagger: 0.025,
  }, startTime);
-->