react17和react18中useReducer为什么会表现不一致？

Question

export default function App() {
  const [count,dispatch] = useReducer((prevState)=>{
    console.log('reducer')
    return prevState+1
  },12)
  return (
    <div className="App">
    <h1 onClick={()=>{
      console.log('dispatch-start')
      dispatch()
      console.log('dispatch-end')
    }}>Hello CodeSandbox{count}</h1>
      <h2>Start editing to see some magic happen!</h2>
    </div>
  );
}

• 在react17中点击h1第一次会打印
  dispatch-start
  reducer
  dispatch-end
  reducer
• 如果再次点击h1会打印
  dispatch-start
  dispatch-end
  reducer
• 如果在react18中每次打印出的都是
  dispatch-start
  dispatch-end
  reducer

这是什么原因呢？

Answer 1

Reactjs的懒计算、立即计算策略。详细参考解密React state hook