```js
// /my-addon/register.js

import React from 'react';

import { useAddonState } from '@storybook/api';

export const Panel = () => {
  const [state, setState] = useAddonState('my/addon-id', 'initial state');

  return <button onClick={() => setState('a new value')}>the state = "{state}"</button>;
};
export const Tool = () => {
  const [state, setState] = useAddonState('my/addon-id', 'initial state');

  return <button onClick={() => setState('a new value')}>the state = "{state}"</button>;
};
```