replaceForContext.js

import React from 'react';

var obj = null;
var listener = null;
function getObj() {
  return obj;
}
function setListener(l) {
  listener = l;
}
function setObj(o) {
  obj = o;
  if (listener) { listener(o); }
}
function Child1() {
  return (
    <div>{JSON.stringify(getObj())}</div>
  )
}
function Chld2() {
  const setRandom = () => {
    setObj({ val: Math.random().toString() });
  }
  return (
    <button onClick={setRandom}>click</button>
  )
}
export default function App() {
  const [, forceUpdate] = React.useReducer(x=>x+1,0);
  React.useEffect(() => {
    setListener((newObj) => {
      forceUpdate();
      console.log(newObj);
    })
  }, [])
  return (
    <div>
      <Child1 />
      <Chld2 />
    </div>
  );
}