Here’s the real kicker, if you’re building an application with React, you already have a state management library installed in your application. You don’t even need to npm install (or yarn add) it. It costs no extra bytes for your users, it integrates with all React packages on npm, and it’s already well documented by the React team. It’s React itself.

React is a state management library.

// src/count/count-context.js
import React from 'react'
const CountContext = React.createContext();

function useCount() {
  const context = React.useContext(CountContext)
  if (!context) {
    throw new Error(`useCount must be used within a CountProvider`);
  }
  return context;
}

function CountProvider(props) {
  const [count, setCount] = React.useState(0);
  const value = React.useMemo(() => [count, setCount], [count]);
  return <CountContext.Provider value={value} {...props} />
}

export {CountProvider, useCount}

// src/count/page.js
import React from 'react'
import {CountProvider, useCount} from './count-context'

function Counter() {
  const [count, setCount] = useCount();
  const increment = () => setCount(c => c + 1);
  return <button onClick={increment}>{count}</button>
}

function CountDisplay() {
  const [count] = useCount();
  return <div>The current counter count is {count}</div>
}

function CountPage() {
  return (
    <div>
      <CountProvider>
        <CountDisplay />
        <Counter />
      </CountProvider>
    </div>
  );
}