explore/lib/hooks/useClientRect.tsx

import _debounce from 'lodash/debounce';
import type { LegacyRef } from 'react';
import React from 'react';

export default function useClientRect<E extends Element>(): [ DOMRect | null, LegacyRef<E> | undefined ] {
  const [ rect, setRect ] = React.useState<DOMRect | null>(null);
  const nodeRef = React.useRef<E>();

  const ref = React.useCallback((node: E) => {
    if (node !== null) {
      setRect(node.getBoundingClientRect());
    }
    nodeRef.current = node;
  }, []);

  React.useEffect(() => {
    const content = window.document.querySelector('main');
    if (!content) {
      return;
    }

    const resizeHandler = _debounce(() => {
      setRect(nodeRef.current?.getBoundingClientRect() ?? null);
    }, 100);

    const resizeObserver = new ResizeObserver(resizeHandler);
    resizeObserver.observe(content);
    resizeObserver.observe(window.document.body);

    return function cleanup() {
      resizeObserver.unobserve(content);
      resizeObserver.unobserve(window.document.body);
    };
  }, [ ]);

  return [ rect, ref ];
}