787 lines
12 KiB
Markdown
787 lines
12 KiB
Markdown
React 备忘清单
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===
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适合初学者的综合 React 备忘清单。
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入门
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----
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### 介绍
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React 是一个用于构建用户界面的 JavaScript 库。
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- [React 官方文档](https://reactjs.org/) _(reactjs.org)_
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```js
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import React from 'react'
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import {createRoot} from 'react-dom/client'
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import App from './App'
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```
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-----
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```jsx
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const elm = document.getElementById('app')
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const root = createRoot(elm);
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root.render(<App />);
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```
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### 导入多个导出
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```jsx
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import React, {Component} from 'react'
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import ReactDOM from 'react-dom'
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```
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-----
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```jsx
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export class Hello extends Component {
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...
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}
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```
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使用 `export` 或者 `export default` 导出 `Hello` 组件
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```jsx
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import { Hello } from './hello.js';
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const Example = <Hello />;
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```
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使用 `import` 导入 `Hello` 组件，在示例中使用。
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### React 组件中的 CSS
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```jsx
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import React from "react";
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import "./Student.css";
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export const Student = (
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<div className="Student"></div>
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);
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```
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注意：类属性 `className`
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```jsx
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const divStyle = {
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backgroundImage: 'url(' + imgUrl + ')',
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};
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export const Student = (
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<div style={divStyle}></div>
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);
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```
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### 属性
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```jsx
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<Student name="Julie" age={23}
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pro={true} />
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```
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函数组件 `Student` 中访问属性
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```jsx
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function Student(props) {
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return <h1>Hello, {props.name}</h1>;
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}
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```
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Class 组件 `Student` 中访问属性
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```jsx
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class Student extends React.Component {
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render() {
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return (
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<h1>Hello, {this.props.name}</h1>
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);
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}
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}
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```
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`class` 组件使用 `this.props` 访问传递给组件的属性。
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### Children
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<!--rehype:wrap-class=row-span-2-->
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```jsx
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function Example() {
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return (
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<AlertBox>
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<h1>您有待处理的通知</h1>
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</AlertBox>
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)
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}
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```
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函数 `AlertBox` 组件
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```jsx
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function AlertBox(props) {
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return (
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<div className="alert-box">
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{props.children}
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</div>
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);
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}
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```
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----
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```jsx
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{props.children}
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```
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Class `AlertBox` 组件，与函数组件 `AlertBox` 组件相同
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```jsx
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class AlertBox extends React.Component {
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render () {
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return (
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<div className="alert-box">
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{this.props.children}
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</div>
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);
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}
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}
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```
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----
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```jsx
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{this.props.children}
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```
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`children` 作为子组件的的属性传递。
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### State
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<!--rehype:wrap-class=row-span-3-->
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函数中的 State，Hook 是 React 16.8 的新增特性
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```jsx
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import { useState } from 'react';
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function Student() {
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// 声明一个叫 "count" 的 state 变量
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const [count, setCount] = useState(0);
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const click = () => setCount(count + 1);
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return (
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<div>
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<p>您点击了 {count} 次</p>
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<button onClick={click}>
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点击我
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</button>
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</div>
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);
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}
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```
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使用 `setState` 更新状态，下面是函数组件读取状态
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```jsx
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<p>您点击了 {count} 次</p>
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```
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#### Class 中的 State
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```jsx
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import React from 'react';
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class Student extends React.Component {
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constructor(props) {
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super(props);
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this.state = {count: 1};
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}
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click() {
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const count = this.state.count;
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this.setState({ count: count + 1})
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}
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render() {
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return (
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<div>
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<button onClick={this.click}>
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点击我
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</button>
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<p>您点击了{this.state.count}次</p>
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</div>
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);
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}
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}
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```
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使用 `setState` 更新状态，`class` 组件中不能使用 <yel>~~hooks~~</yel>。下面是 `class` 组件读取状态
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```jsx
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<p>您点击了{this.state.count}次</p>
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```
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### 循环
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```jsx
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const elm = ['one', 'two', 'three'];
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function Student() {
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return (
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<ul>
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{elm.map((value, index) => (
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<li key={index}>{value}</li>
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))}
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</ul>
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);
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}
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```
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`key` 值在兄弟节点之间必须唯一
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### 事件监听
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```jsx
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export default function Hello() {
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function handleClick(event) {
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event.preventDefault();
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alert("Hello World");
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}
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return (
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<a href="/" onClick={handleClick}>
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Say Hi
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</a>
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);
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}
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```
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### 函数注入
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```jsx
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function addNumbers(x1, x2) {
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return x1 + x2;
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}
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const element = (
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<div>{addNumbers(2, 5)}</div>
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)
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```
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### 嵌套
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```jsx
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import { useState } from 'react'
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import Avatar from './Avatar';
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import Profile from './Profile';
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function Student() {
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const [count, setCount] = useState(0);
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return (
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<div>
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<Avatar src={count} />
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<Profile username={count} />
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</div>
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);
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}
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```
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### Fragment
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```jsx
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import { Fragment } from 'react'
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import Avatar from './Avatar';
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import Profile from './Profile';
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const Student = () => (
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<Fragment>
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<Avatar src="./demo.jpg" />
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<Profile username="name" />
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</Fragment>
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)
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```
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从 @v16.2.0 开始，`Fragment` 可用于返回多个子节点，而无需向 DOM 添加额外的包装节点。
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### Portals
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React 并*没有*创建一个新的 `div`。它只是把子元素渲染到 `domNode` 中。`domNode` 是一个可以在任何位置的有效 DOM 节点。
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```jsx
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render() {
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return ReactDOM.createPortal(
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this.props.children,
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domNode
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);
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}
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```
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提供了一种将子节点渲染到存在于父组件以外的 DOM 节点的优秀的方案
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默认值
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---
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### Class 组件默认 props
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<!--rehype:wrap-class=row-span-2-->
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```jsx
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class CustomButton extends React.Component {
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// ...
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}
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CustomButton.defaultProps = {
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color: 'blue'
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};
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```
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#### 使用
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```jsx
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<CustomButton /> ;
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```
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不传值 `props.color` 将自动设置为 `blue`
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### Class 组件默认 state
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<!--rehype:wrap-class=row-span-2-->
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```jsx
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class Hello extends Component {
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constructor (props) {
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super(props)
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this.state = { visible: true }
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}
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}
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```
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在构造 `constructor()`中设置默认状态。
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```jsx
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class Hello extends Component {
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state = { visible: true }
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}
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```
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### 函数组件默认 props
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```jsx
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function CustomButton(props) {
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const { color = 'blue' } = props;
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return <div>{color}</div>
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}
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```
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### 函数组件默认 state
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```jsx
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function CustomButton() {
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const [color, setColor]=useState('blue')
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return <div>{color}</div>
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}
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```
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JSX
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---
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### 介绍
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<!--rehype:wrap-class=row-span-2-->
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`JSX` 仅仅只是 `React.createElement(component, props, ...children)` 函数的语法糖
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```jsx
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<MyButton color="blue" shadowSize={2}>
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点击我
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</MyButton>
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```
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会编译为
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```js
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React.createElement(
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MyButton,
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{color: 'blue', shadowSize: 2},
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'点击我'
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);
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```
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没有子节点
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```jsx
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<div className="sidebar" />
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```
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会编译为
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```js
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React.createElement(
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'div',
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{className: 'sidebar'}
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)
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```
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### JSX 点语法
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```jsx
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const Menu = ({ children }) => (
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<div className="menu">{children}<div>
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);
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Menu.Item = ({ children }) => (
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<div>{children}<div>
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);
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<Menu>
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<Menu.Item>菜单一</Menu.Item>
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<Menu.Item>菜单二</Menu.Item>
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<Menu>
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```
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### JSX Element
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```jsx
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let element = <h1>Hello, world!</h1>;
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let emptyHeading = <h1 />;
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const root = ReactDOM.createRoot(
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document.getElementById('root')
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);
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const element = <h1>Hello, world</h1>;
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root.render(element);
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```
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参考：[渲染元素](https://reactjs.org/docs/rendering-elements.html)
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### JSX 属性
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```jsx
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const element = (
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<img src={user.avatarUrl} />
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);
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const element = (
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<button className="btn">
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点击我
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</button>
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);
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```
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注意：类属性 `className`
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### JSX 表达式
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```jsx
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let name = 'Josh Perez';
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let element = <h1>Hello, {name}</h1>;
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function fullName(firstName, lastName) {
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return firstName + ' ' + lastName;
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}
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let element = (
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<h1>
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Hello, {fullName('Julie', 'Johnson')}
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</h1>
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);
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```
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### JSX style
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```jsx
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const divStyle = {
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color: 'blue',
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backgroundImage: 'url(' + imgUrl + ')',
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};
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function MyComponent() {
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return <div style={divStyle}>组件</div>;
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}
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```
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### JSX dangerouslySetInnerHTML
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```jsx
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const markup = {__html: '我 · 你' };
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const MyComponent = () => (
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<div dangerouslySetInnerHTML={markup} />
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);
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```
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`dangerouslySetInnerHTML` 是 React 为浏览器 DOM 提供 `innerHTML` 的替换方案。
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### JSX htmlFor
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```jsx
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const MyComponent = () => (
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<div>
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<input type="radio" id="ab" name="v">
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<label for="ab">HTML</label>
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</div>
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);
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```
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`for` 在 `JS` 中是保留字，JSX 元素使用了 `htmlFor` 代替
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### JSX defaultValue
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非受控组件的属性，设置组件第一次挂载时的 `value`
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```jsx
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<textarea defaultValue="Hello" />
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```
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`<input>`、`<select>` 和 `<textarea>` 支持 value 属性
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### JSX defaultChecked
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非受控组件的属性，设置组件是否被选中
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```jsx
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<input type="radio" defaultChecked />
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```
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类型为 `checkbox` 或 `radio` 时，组件支持 checked 属性
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### JSX className
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属性用于指定 `CSS` 的 `class`
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```jsx
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<div className="warp">...</div>
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```
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React 中使用 [Web Components](https://developer.mozilla.org/zh-CN/docs/Web/Web_Components) 使用 `class` 属性代替
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### JSX 条件渲染
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<!--rehype:wrap-class=row-span-2-->
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```jsx
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import React from "react";
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function formatName(user) {
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return user.firstName
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+ ' '
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+ user.lastName;
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}
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export function Greeting(user) {
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if (user) {
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return (
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<h1>你好, {formatName(user)}!</h1>
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);
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}
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return (
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<h1>你好, 先生。</h1>
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);
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}
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```
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注意：组件必须总是返回一些东西。
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#### 使用
|
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```jsx
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<Greeting firstName="三" lastName="张" />
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```
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### JSX 三目运算符 / 与运算符 &&
|
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|
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```jsx
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export default function Weather(props) {
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const isLoggedIn = props.isLoggedIn;
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return (
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<div>
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<b>{isLoggedIn ? '已' : '未'}</b>登录。
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</div>
|
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);
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}
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```
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----
|
||
|
||
```js
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{isShow && <div>内容</div>}
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```
|
||
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### JSX 组件
|
||
|
||
```jsx
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||
<Dropdown>
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下拉列表
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||
<Menu>
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<Menu.Item>菜单一</Menu.Item>
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<Menu.Item>菜单二</Menu.Item>
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<Menu.Item>菜单三</Menu.Item>
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</Menu>
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</Dropdown>
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```
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组件名称以大驼峰式命名。
|
||
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### JSX 元素变量
|
||
|
||
```jsx
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function Greeting(props) {
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let button;
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if (props.isLoggedIn) {
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button = <UserGreeting />;
|
||
} else {
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button = <GuestGreeting />;
|
||
}
|
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return <div>{button}</div>;
|
||
}
|
||
```
|
||
|
||
### JSX 注释
|
||
|
||
```jsx
|
||
function Student() {
|
||
const [count, setCount] = useState(0);
|
||
return (
|
||
<Fragment>
|
||
{/* 这里写注释 */}
|
||
</Fragment>
|
||
);
|
||
}
|
||
```
|
||
|
||
组件
|
||
----
|
||
|
||
### 函数组件
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
```jsx
|
||
import React from 'react';
|
||
|
||
const UserName = () => <h1>Kenny</h1>;
|
||
|
||
export default function UserProfile() {
|
||
return (
|
||
<div className="UserProfile">
|
||
<div>Hello</div>
|
||
<UserName />
|
||
</div>
|
||
);
|
||
}
|
||
```
|
||
|
||
注意：每个组件都需要一个根元素，[更多说明](https://reactjs.org/docs/components-and-props.html)。
|
||
|
||
### Class 组件
|
||
|
||
```jsx
|
||
class Welcome extends React.Component {
|
||
render() {
|
||
return <h1>{this.props.name}</h1>;
|
||
}
|
||
}
|
||
```
|
||
|
||
### Class 组件 API
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
#### 额外的 API
|
||
|
||
:- | -
|
||
:- | -
|
||
`this.forceUpdate()` | 强制重新渲染
|
||
`this.setState({ ... })` | 更新状态
|
||
`this.setState(state =>{ ... })` | 更新状态
|
||
|
||
#### 属性
|
||
|
||
:- | -
|
||
:- | -
|
||
`defaultProps` | 默认 props
|
||
`displayName` | 显示组件名称(用于调试)
|
||
|
||
#### 实例属性
|
||
|
||
:- | -
|
||
:- | -
|
||
`this.props` | 组件接受参数
|
||
`this.state` | 组件内状态
|
||
|
||
|
||
### Pure 组件
|
||
|
||
```jsx
|
||
import React, {PureComponent} from 'react'
|
||
|
||
class MessageBox extends PureComponent {
|
||
···
|
||
}
|
||
```
|
||
### 嵌入内部组件
|
||
|
||
```jsx
|
||
import React from 'react';
|
||
import UserAvatar from "./UserAvatar";
|
||
|
||
export default function UserProfile() {
|
||
return (
|
||
<div className="UserProfile">
|
||
<UserAvatar />
|
||
<UserAvatar />
|
||
</div>
|
||
);
|
||
}
|
||
```
|
||
|
||
注意：假设 `UserAvatar` 在 `UserAvatar.js` 中声明。
|
||
|
||
### 嵌入外部组件
|
||
|
||
```jsx
|
||
import React from 'react';
|
||
import CompName from 'component-name';
|
||
|
||
export default function UserProfile() {
|
||
return (
|
||
<div className="UserProfile">
|
||
<CompName />
|
||
</div>
|
||
);
|
||
}
|
||
```
|
||
|
||
注意：外部组件在 [npmjs.com](https://www.npmjs.com) 上找到，需要先安装导入。
|
||
|
||
### 高阶组件
|
||
|
||
```jsx
|
||
import React, { Component } from 'react';
|
||
// 高阶组件 with
|
||
const with = data => WrappedComponent => {
|
||
return class extends Component {
|
||
constructor(props) {
|
||
super(props);
|
||
}
|
||
render() {
|
||
return (
|
||
<WrappedComponent data={data} />
|
||
)
|
||
}
|
||
}
|
||
}
|
||
```
|
||
|
||
使用高阶组件
|
||
|
||
```jsx
|
||
const LowComponent = (props) => (
|
||
<div>{props.data}</div>
|
||
);
|
||
|
||
const MyComp = with('Hello')(LowComponent)
|
||
```
|
||
|
||
生命周期
|
||
---
|
||
|
||
Hooks
|
||
---
|
||
|
||
|
||
另见
|
||
----
|
||
|
||
- [反应生命周期方法图](https://projects.wojtekmaj.pl/react-lifecycle-methods-diagram/) |