reactSharedMutableStateHook.js

import { useState, useEffect } from 'react';

function sharedState(getState) {
  const setters = new Set();
  return [
    () => {
      const currentState = getState();
      const setter = useState(currentState)[1];
      useEffect(() => {
        setters.add(setter);
        return () => setters.delete(setter);
      }, []);
      return currentState;
    },
    action => (...args) => {
      const result = action(...args);
      setters.forEach(setter => setter(getState));
      return result;
    }
  ];
}

// example
const [useSharedCount, setAction] = sharedState(() => state);

const state = {
  a: {
    b: 0
  }
};
const increment = setAction(() => {
  state.a.b++;
});
const decrement = setAction(() => {
  state.a.b--;
});
const setCount = setAction(value => {
  state.a.b = value;
});

export {
  useSharedCount,
  increment,
  decrement,
  setCount
};