_computeTargetAndRootIntersection()

in packages/appear/src/web/intersection-observer.ts [318:360]
32 lines of code
12 McCabe index (conditional complexity)

  _computeTargetAndRootIntersection(target, rootRect) {
    // If the element isn't displayed, an intersection can't happen.
    if (window.getComputedStyle(target).display == 'none') return;

    let targetRect = getBoundingClientRect(target);
    let intersectionRect = targetRect;
    let parent = getParentNode(target);
    let atRoot = false;

    while (!atRoot) {
      let parentRect = null;
      let parentComputedStyle = parent.nodeType == 1
        ? window.getComputedStyle(parent) : {};

      // If the parent isn't displayed, an intersection can't happen.
      if (parentComputedStyle.display === 'none') return;

      if (parent === this.root || parent === document) {
        atRoot = true;
        parentRect = rootRect;
      } else {
        // If the element has a non-visible overflow, and it's not the <body>
        // or <html> element, update the intersection rect.
        // Note: <body> and <html> cannot be clipped to a rect that's not also
        // the document rect, so no need to compute a new intersection.
        if (parent !== document.body &&
          parent !== document.documentElement &&
          parentComputedStyle.overflow !== 'visible') {
          parentRect = getBoundingClientRect(parent);
        }
      }

      // If either of the above conditionals set a new parentRect,
      // calculate new intersection data.
      if (parentRect) {
        intersectionRect = computeRectIntersection(parentRect, intersectionRect);

        if (!intersectionRect) break;
      }
      parent = getParentNode(parent);
    }
    return intersectionRect;
  }