Performant and comprehensive rewrite (Rev 1 is BEFORE, Rev 2+ is AFTER) of `isVisible` in Price Tracker (https://github.com/mozilla/price-tracker/)

isVisible.js

// Avoid reading `display: none` due to Bug 1381071
isVisible(fnode) {
  const element = fnode.element;
  if (element.getBoxQuads().length === 0) {
    // The element has no box (display: none subtree?), checking
    // getBoundingClientRect instead for a width and height of 0 only tells
    // us it is a zero-sized box.
    return false;
  }
  const eleStyle = getComputedStyle(element);
  if (eleStyle.visibility === 'hidden') {
    return false; // not painted.
  }
  // This is assuming inclusive ancestors, otherwise we need to check opacity
  // above too.
  for (const ancestor of ancestors(element)) {
    const style = getComputedStyle(ancestor);
    if (style.opacity === '0') {
      return false;
    }
    if (style.display === 'contents') {
      // display: contents elements have no box themselves, but children are
      // still rendered.
      continue;
    }
    const rect = ancestor.getBoundingClientRect();
    if ((rect.width === 0 || rect.height === 0) && style.overflow === 'hidden') {
      // This is a zero-sized box; zero-sized ancestors don’t make descendants
      // hidden unless the descendant has overflow: hidden
      return false;
    }
  }
  return true;
}

eleStyle should be style, it's the zero-sized box which needs overflow: hidden to actually hide it.

Thanks!