const useCounter = () => {

  const [count, setCount] = React.useState(0)

  React.useEffect(() => {

    const interval = setInterval(() => {

      setCount(previous => previous + 1)

    }, 1000)

    return () => {

      clearInterval(interval)

    }

  }, [])

  return count

}

​

function App () {

  const count = useCounter()

​

  return (

    <div>{count}</div>

  )

}