react/basic/6/P06.html

<!--
 * @Author: chenxuan
 * @Date: 2022-01-13 22:59:55
 * @LastEditTime: 2022-01-13 23:14:43
 * @LastEditors: chenxuan
-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>getSnapshotBeforeUpdate</title>
    <script src="../package/new/react.development.js"></script>
    <script src="../package/new/react-dom.development.js"></script>
    <script src="../package/new/babel.min.js"></script>
</head>
<body>
    <div id="app"></div>
    <script type="text/babel">
        class Count extends React.Component{
            constructor(props){
                console.log("1-constructor")
                super(props)
                this.state={count:100}
            }
            
            add=()=>{
                let {count}=this.state;
                count+=1;
                this.setState({count})
            }
            render(){
                console.log("3-render")
                return (
                    <div>
                        <h2>当前求和为：{this.state.count}</h2>
                        <button onClick={this.add}>点我+1</button>
                    </div>
                )
            }
            componentDidMount(){
                console.log('4-componentDidMount')
            }
            componentWillUnmount(){
                console.log("5-componentWillUnmount")
            }
            // 控制组件更新的阀门
            shouldComponentUpdate(){
                console.log('shouldComponentUpdate') 
                return true
            }
            // 组件更新之前搞一些事情
            // 次钩子函数的任何值都会传递给componentDidUpdate
            getSnapshotBeforeUpdate(prevProps,prevState){
                // console.log(preState)
                return "getSnapshotBeforeUpdate"
            }
            componentDidUpdate(preProps,preState,snapshotValue){
                // console.log(snapshotValue)
                console.log(preProps,preState)
                // console.log('componentDidUpdate') 
            }
        }
        ReactDOM.render(
			<Count count={1999} />,document.getElementById('app')
		)
    </script>
</body>
</html>