useResizeObserver.ts

import { useMemo, useEffect, MutableRefObject } from 'react';

export default function useResizeObserver(
  targetNode: MutableRefObject<any>,
  callback: (rect: DOMRect) => void,
) {
  const observer = useMemo(
    () =>
      // Note: ResizeObserver comes back as unfound even
      // this it's available, so for now I'm just going to
      // ignore the error
      // @ts-ignore
      new ResizeObserver((entries) => {
        for (const entry of entries) {
          callback(entry.contentRect);
        } 
      }),
    [callback]
  );

  useEffect(
    () => {
      if (targetNode.current) {
        observer.observe(targetNode.current);

        return () => {
          observer.disconnect();
        };
      }
      return;
    },
    [targetNode.current]
  );
}

// We need to push the list down based on the current size of
// the banner, which can change because the window is resizable
const resizeCallback = React.useCallback((rect) => {
  if (listRef.current) {
    listRef.current.style.transform = `translateY(${rect.height + OFFSET}px)`;
  }
}, [listRef]);


React.useEffect(() => {
  return () => {
    // Reset the FileList bump when the banner is unmounted
    listRef.current.style.transform = `translateY(0px)`;
  };
}, []);