9. 生命周期

src/components/SonComponent.js

@@ -2,33 +2,61 @@ import React from "react";
 import PropTypes from "proptypes"
 // 模块化 css, 后缀 .module.css
 import SonComponentCss from "./SonComponent.module.css"
-export default class SonComponent extends React.PureComponent {
+export default class SonComponent extends React.Component {
     state = {
         msg: "SonComponent Msg",
         showChildrenBorder: true,
         childrenClass: []
     }
 
-    // constructor(props) {
+    constructor(props) {
-    //     super(props);
+        super(props);
-    //     console.log(props)
+        console.log("[constructor] SonComponent")
-    // }
+    }
 
+    // 相当于 vue mounted
     componentDidMount() {
         this.changeChildrenClass()
         console.log('[挂载] SonComponent 组件后执行的操作');
     }
 
+    // 优化生命周期
+    // 手动实现 类似 React.PureComponent 的功能
+    // 如果返回值为 false 则不会调用 render 更新组件
+    shouldComponentUpdate(nextProps, nextState, nextContext) {
+        console.log("[shouldComponentUpdate] SonComponent")
+        console.log("修改前 => ", this.state, "修改后 =>", nextState)
+
+        // 是否需要更新组件
+        // return !Object.keys(this.state).reduce((prev,key)=> {
+        //     return prev?this.state[key] === nextState[key]:prev;
+        // }, true)
+        for(let key in this.state){
+            console.log(key, this.state[key], nextState[key], this.state[key] !== nextState[key])
+            if(this.state[key] !== nextState[key]){
+                return true;
+            }
+        }
+        return false;
+    }
+
+    // 相当于 vue updated
     componentDidUpdate(prevProps, prevState, snapshot) {
         // 当count更新时执行的操作
-        console.log('SonComponent 组件后更新，执行的操作:', this.state);
+        console.log('[componentDidUpdate] SonComponent 组件后更新，执行的操作:', this.state);
     }
 
 
+    // 相当于 vue unmount
     componentWillUnmount() {
         console.log('[卸载] SonComponent 组件 前执行的操作');
     }
 
+    static getDerivedStateFromProps(props, state){
+        console.log("[getDerivedStateFromProps] SonComponent", props, state)
+        return null
+    }
+
     switchChildrenBorder = () => {
         this.setState({
             ...this.state,
@@ -51,6 +79,7 @@ export default class SonComponent extends React.PureComponent {
     }
 
     render() {
+        console.log("[render] SonComponent")
         return <div style={{border: '1px solid', width: '80%', overflow: 'auto'}}>
             子组件
 

src/components/SonComponent2.js

@@ -35,9 +35,10 @@ export default function SonComponent2(props= {
     }
 
     function revokeChangeMsg(){
+        let count = state.count
         setState({
             ...state,
-            // count: state.count > 0 ? --state.count : 0,
+            count: count > 0 ? --count : 0,
             tmp: props.changeMsg(state.tmp)
         })
     }

src/index.js

@@ -6,9 +6,14 @@ import reportWebVitals from './reportWebVitals';
 
 const root = ReactDOM.createRoot(document.getElementById('root'));
 root.render(
-  <React.StrictMode>
+    /**
-    <App />
+     *  严格模式: 只在开发模式中生效, 打包后会去除
-  </React.StrictMode>
+     *  检测危险操作, 比如废弃和不推荐的api
+     *  重复执行2次生命周期函数, 检测额外的副作用 如 render
+     */
+    // <React.StrictMode>
+    <App/>
+    // </React.StrictMode>
 );
 
 // If you want to start measuring performance in your app, pass a function