text: import React from 'react'
  const Counter = ({count, add, subtract, addAsync, subtractAsync}) => (
    <div>
      <h1>{count}</h1>
      <button onClick={add}>+</button>
      <button onClick={subtract}>-</button>
      <br />
      <button onClick={addAsync}>延时 +</button>
      <button onClick={subtractAsync}>延时 -</button>
    </div>
  )
  export default Counter