Function overflowingAncestor

scripts/smoothScroll.js:633–662

(el, x)

  // scroll  |   no   |   YES   |   YES  |   YES  |
  // auto    |   no   |   YES   |   YES  |   YES  |
  function overflowingAncestor(el, x) {
    let elems = [];
    let body = document.body;
    let rootScrollHeight = root.scrollHeight;
    let rootScrollWidth = root.scrollWidth;
    do {
      let cached = getCache(el, x);
      if (cached) {
        return setCache(elems, cached, x);
      }
      elems.push(el);
      if (
        (x && rootScrollWidth === el.scrollWidth) ||
        (!x && rootScrollHeight === el.scrollHeight)
      ) {
        let topOverflowsNotHidden =
          overflowNotHidden(root, x) && overflowNotHidden(body, x);
        let isOverflowCSS =
          topOverflowsNotHidden || overflowAutoOrScroll(root, x);
        if (
          (isFrame && isContentOverflowing(root, x)) ||
          (!isFrame && isOverflowCSS)
        ) {
          return setCache(elems, getScrollRoot(), x);
        }
      } else if (isContentOverflowing(el, x) && overflowAutoOrScroll(el, x)) {
        return setCache(elems, el, x);
      }
    } while ((el = el.parentElement));
  }
  function isContentOverflowing(el, x) {
    return x
      ? el.clientWidth + 10 < el.scrollWidth