import React, { useState } from "react";

let ChildComponent = ({ setRef }) => <div ref={setRef}>{/* content */}</div>;

let ParentComponent = () => {
  let [ref, setRef] = useState();

  useEffect(() => {
    if (ref) {
      // whatever you want to use ref for
    }
  }, [ref]);

  return <ChildComponent setRef={setRef} />;
};