@restart/hooks/esm/useResizeObserver.js

import { useState } from 'react';
import useEffect from './useIsomorphicEffect';
const targetMap = new WeakMap();
let resizeObserver;
function getResizeObserver() {
  // eslint-disable-next-line no-return-assign
  return resizeObserver = resizeObserver || new window.ResizeObserver(entries => {
    entries.forEach(entry => {
      const handler = targetMap.get(entry.target);
      if (handler) handler(entry.contentRect);
    });
  });
}

/**
 * Efficiently observe size changes on an element. Depends on the `ResizeObserver` api,
 * and polyfills are needed in older browsers.
 *
 * ```ts
 * const [ref, attachRef] = useCallbackRef(null);
 *
 * const rect = useResizeObserver(ref);
 *
 * return (
 *  <div ref={attachRef}>
 *    {JSON.stringify(rect)}
 *  </div>
 * )
 * ```
 *
 * @param element The DOM element to observe
 */
export default function useResizeObserver(element) {
  const [rect, setRect] = useState(null);
  useEffect(() => {
    if (!element) return;
    getResizeObserver().observe(element);
    setRect(element.getBoundingClientRect());
    targetMap.set(element, rect => {
      setRect(rect);
    });
    return () => {
      targetMap.delete(element);
    };
  }, [element]);
  return rect;
}