React使用JSX语法 | 易学教程

1、在React项目中启用JSX语法

2、在JSX中写js代码

1、在React项目中启用JSX语法

　　JSX语法：符和xml规范的js语法

　　JSX语法的本质：在运行时，转换成React.createElement形式来执行

　　第一步：安装babel插件:

cnpm i babel-core babel-loader babel-plugin-transform-runtime -D
cnpm i babel-preset-env babel-preset-stage-0 babel-preset-react -D

　　第二步：webpack.config.js

var path = require('path')

// 导入在内存中自动生成index页面的插件
const HtmlWebPackPlugin = require('html-webpack-plugin')
const htmlPlugin = new HtmlWebPackPlugin({
    template: path.join(__dirname, './src/index.html'),
    filename: 'index.html' // 生成的内存中首页的名称
});

module.exports = {
    mode: 'development',
    plugins: [
        htmlPlugin
    ],
    module: {
        rules:[
            { test:/\.js|jsx$/, use: ['babel-loader'], exclude: /node_modules/ }
        ]
    }
}

　　第三步：添加.babelrc配置文件

{
    "presets": ["env", "stage-0", "react"],
    "plugins": ["transform-runtime"]
}

　　第四步：index.js使用JSX语法

import React from 'react'
import ReactDOM from 'react-dom'

// 创建虚拟DOM元素
// 参数1: 元素名称; 参数2: 属性; 参数3-n: 子节点
// const myh1 = React.createElement('h1', {id: 'myh1'}, 'h1标签的文本')
// const mydiv = React.createElement('div', null, 'div文本', myh1) // div中包含了h1
const mydiv = <div id="mydiv">测试JSX语法</div>
// 将虚拟DOM渲染到页面
// 参数1: 虚拟DOM元素; 参数2: 容器
ReactDOM.render(mydiv, document.getElementById('app'))

　　第五步：npm run dev

　　走完上面五步，package.json：

{
  "name": "webpack4.x-base",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "dev": "webpack-dev-server --open --port 3000 --hot --host 127.0.0.1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "babel-core": "^6.26.3",
    "babel-loader": "^8.0.6",
    "babel-plugin-transform-runtime": "^6.23.0",
    "babel-preset-env": "^1.7.0",
    "babel-preset-react": "^6.24.1",
    "babel-preset-stage-0": "^6.24.1",
    "html-webpack-plugin": "^3.2.0",
    "webpack": "^4.41.2",
    "webpack-cli": "^3.3.10",
    "webpack-dev-server": "^3.9.0"
  },
  "dependencies": {
    "react": "^16.12.0",
    "react-dom": "^16.12.0"
  }
}

　　结果报错：

　　解决：

　　卸载babel-loader@8

cnpm un babel-loader

　　安装babel-loader@7，（安装"babel-loader": "^7.1.5"）

cnpm i babel-loader@7 -D

2、在JSX中写js代码

　　使用变量

import React from 'react'
import ReactDOM from 'react-dom'

const msg = "hello";
const mydiv = <div id="mydiv">{msg}测试JSX语法</div>
ReactDOM.render(mydiv, document.getElementById('app'))

　　表达式

const a = 10;
const mydiv = <div id="mydiv">{a + 2}测试JSX语法</div>
ReactDOM.render(mydiv, document.getElementById('app'))

　　三元表达式

const flag = true;
const mydiv = <div id="mydiv">{flag ? '真' : '假'}测试JSX语法</div>
ReactDOM.render(mydiv, document.getElementById('app'))

来源：https://www.cnblogs.com/xy-ouyang/p/11992882.html

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