当前未启用对实验语法“classProperties”的支持

Question

我在 Django 项目中设置 React 时遇到了这个错误

ModuleBuildError 在 模块构建失败（来自 ./node_modules/babel-loader/lib/index.js）： 语法错误：C:\Users\1Sun\Cebula3\cebula_react\assets\js\index.js：支持 对于实验性语法“classProperties”当前未启用 (17:9)：

  15 | 
  16 | class BodyPartWrapper extends Component {
> 17 |   state = {
     |         ^
  18 | 
  19 |   }
  20 | 

Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 
'plugins' section of your Babel config to enable transformation.

所以，我安装了 @babel/plugin-proposal-class-properties 并将其放入 babelrc

package.json

{
  "name": "cebula_react",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "webpack-dev-server --config ./webpack.config.js --mode development",
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "webpack --config prod.config.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "babel": {
    "presets": [
      "@babel/preset-env",
      "@babel/preset-react"
    ]
  },
  "devDependencies": {
    "@babel/cli": "^7.0.0",
    "@babel/core": "^7.0.0",
    "@babel/plugin-proposal-class-properties": "^7.0.0",
    "@babel/preset-env": "^7.0.0",
    "@babel/preset-react": "^7.0.0",
    "babel-loader": "^8.0.2",
    "babel-plugin-transform-class-properties": "^6.24.1",
    "react-hot-loader": "^4.3.6",
    "webpack": "^4.17.2",
    "webpack-bundle-tracker": "^0.3.0",
    "webpack-cli": "^3.1.0",
    "webpack-dev-server": "^3.1.8"
  },
  "dependencies": {
    "react": "^16.5.0",
    "react-dom": "^16.5.0"
  }
}

babelrc

{
  "presets": [
    "@babel/preset-env",
    "@babel/preset-react"
  ],
  "plugins": [
    "@babel/plugin-proposal-class-properties"
  ]
}

但是错误依旧存在，请问是什么问题？

Answer 1

改变

"plugins": [
    "@babel/plugin-proposal-class-properties"
  ]

收件人

"plugins": [
    [
      "@babel/plugin-proposal-class-properties",
      {
        "loose": true
      }
    ]
  ]

这对我有用

Answer 2

首先安装：@babel/plugin-proposal-class-properties作为开发依赖：

npm install @babel/plugin-proposal-class-properties --save-dev

然后编辑您的 .babelrc，使其完全像这样：

{
  "presets": [
      "@babel/preset-env",
      "@babel/preset-react"
  ],
  "plugins": [
      [
        "@babel/plugin-proposal-class-properties"
      ]
  ]
}

.babelrc 文件位于根目录，package.json 所在的位置。

请注意，您应该重新启动 webpack 开发服务器以使更改生效。

Answer 3

webpack 项目解决方案

我只是通过在 webpack 配置插件中添加 @babel/plugin-proposal-class-properties 来解决这个问题。 我的webpack.config.js 的模块部分是这样的

module: {
    rules: [
        {
            test: path.join(__dirname, '.'),
            exclude: /(node_modules)/,
            loader: 'babel-loader',
            options: {
                presets: ['@babel/preset-env',
                          '@babel/react',{
                          'plugins': ['@babel/plugin-proposal-class-properties']}]
            }
        }
    ]
}

Answer 4

{
    "presets": [
        "@babel/preset-env",
        "@babel/preset-react"
    ],
    "plugins": [
        [
          "@babel/plugin-proposal-class-properties"
        ]
    ]
}

用上面的代码替换你的 .babelrc 文件。它为我解决了这个问题。

Answer 5

在我的工作环境根目录中，.babelrc 文件不存在。但是，在 package.json 中的以下条目解决了这个问题。

"babel": {
"presets": [
  "@babel/preset-env",
  "@babel/preset-react"
],
"plugins": [
  "@babel/plugin-proposal-class-properties"
]}

注意：在执行 npm 或 yarn 命令之前，不要忘记退出控制台并重新打开。

Answer 6

有两种方法可以处理反应状态：

选项 1： 只需添加到 package.json：

"babel": {
        "presets": [
            "@babel/preset-env",
            "@babel/preset-react"
        ],
        "plugins": [
            "@babel/plugin-proposal-class-properties"
        ]
    }

选项 2：

1.在根文件夹中创建一个名为 .babelrc 的文件。

写入.babelrc：

{ "plugins": ["@babel/plugin-proposal-class-properties"] }

1. 运行：

npm i @babel/plugin-proposal-class-properties

3.运行：

npm run dev
or
npm run watch

Answer 7

在同一错误上搜索并花费了将近 3 个小时后，我发现我正在为 React 使用名称导入：

import { React } from 'react';

这是完全错误的。只需将其切换为：

import React from 'react';

所有错误都消失了。 我希望这可以帮助别人。这是我的 .babelrc：

{
  "presets": [
    "@babel/preset-env",
    "@babel/preset-react"
  ],
  "plugins": [
      "@babel/plugin-proposal-class-properties"
  ]
}

webpack.config.js

const path = require('path');
const devMode = process.env.Node_ENV !== 'production';
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
module.exports = {
  entry: './src/App.js',
  devtool: 'source-map',
  output: {
    path: path.resolve(__dirname, 'public'),
    filename: 'App.js'
  },
  mode: 'development',
  devServer: {
    contentBase: path.resolve(__dirname, 'public'),
    port:9090,
    open: 'google chrome',
    historyApiFallback: true
  },
  module: {
    rules: [
      {
        test: /\.m?js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader'
        }
      },{
        test: /\.(sa|sc|c)ss$/,
        use: [
          devMode ? 'style-loader' : MiniCssExtractPlugin.loader,
          {
            loader: 'css-loader',
            options: {
              modules: true,
              localIdentName: '[local]--[hash:base64:5]',
              sourceMap: true
            }
          },{
            loader: 'sass-loader'
          }
        ]
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      filename: devMode ? '[name].css' : '[name].[hash].css',
      chunkFilename: devMode ? '[id].css' : '[id].[hash].css'
    })
  ]
}

package.json

{
  "name": "expense-app",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "webpack",
    "serve": "webpack-dev-server"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@babel/cli": "^7.1.2",
    "@babel/core": "^7.1.2",
    "@babel/plugin-proposal-class-properties": "^7.1.0",
    "@babel/preset-env": "^7.1.0",
    "@babel/preset-react": "^7.0.0",
    "babel-loader": "^8.0.4",
    "css-loader": "^1.0.0",
    "mini-css-extract-plugin": "^0.4.3",
    "node-sass": "^4.9.3",
    "react-router-dom": "^4.3.1",
    "sass-loader": "^7.1.0",
    "style-loader": "^0.23.1",
    "webpack": "^4.20.2",
    "webpack-cli": "^3.1.2",
    "webpack-dev-server": "^3.1.9"
  },
  "dependencies": {
    "normalize.css": "^8.0.0",
    "react": "^16.5.2",
    "react-dom": "^16.5.2"
  }
}

Answer 8

我发现我的.babelrc 被忽略的问题，但是我创建babel.config.js 并添加以下内容：

module.exports = {
  plugins: [
    ['@babel/plugin-proposal-decorators', { legacy: true }],
    ['@babel/plugin-proposal-class-properties', { loose: true }],
    '@babel/plugin-syntax-dynamic-import',
    '@babel/plugin-transform-regenerator',
    [
      '@babel/plugin-transform-runtime',
      {
        helpers: false,
        regenerator: true,
      },
    ],
  ],
  presets: [
    "@babel/preset-flow",
    'module:metro-react-native-babel-preset',
  ],
};

它适用于 React Native 应用程序，我认为这也将有助于 React 应用程序。

Answer 9

在constructor function 中移动state 对我有用：

...
class MyComponent extends Component {
  constructor(man) {
    super(man)
    this.state = {}
  }
}
...

祝你好运……

Answer 10

• 安装 plugin-proposal-class-properties npm install @babel/plugin-proposal-class-properties --save-dev

• 通过添加更新您的 webpack.config.js 'plugins': ['@babel/plugin-proposal-class-properties']}]

Answer 11

根据this GitHub 问题，如果您使用create-react-app，您应该将您的.babelrc 或babel.config.js 配置复制到webpack.config.js 并删除那些。因为htis 两行代码babelrc: false,configFile: false, 您的配置在 babelrc 中，.. 没用。 并且您的 webpack.config.js 在您的 ./node_madules/react-scripts/config 文件夹中 我这样解决了我的问题：

{
              test: /\.(js|mjs)$/,
              exclude: /@babel(?:\/|\\{1,2})runtime/,
              loader: require.resolve('babel-loader'),
              options: {
                babelrc: false,
                configFile: false,
                compact: false,
                presets: [
                  [
                    require.resolve('babel-preset-react-app/dependencies'),
                    { helpers: true },

                  ],
                  '@babel/preset-env', '@babel/preset-react'
                ],
                plugins: ['@babel/plugin-proposal-class-properties'],
                .
                .
                .

Answer 12

我明确地使用了 babel 解析器。以上解决方案都不适合我。这行得通。

const ast = parser.parse(inputCode, {
      sourceType: 'module',
      plugins: [
        'jsx',
        'classProperties', // '@babel/plugin-proposal-class-properties',
      ],
    });

Answer 13

我正在使用纱线。我必须执行以下操作才能克服错误。

yarn add @babel/plugin-proposal-class-properties --dev

Answer 14

添加

"plugins": [
    [
      "@babel/plugin-proposal-class-properties"
    ]
  ]

进入.babelrc 为我工作。

Answer 15

yarn add --dev @babel/plugin-proposal-class-properties

或

npm install @babel/plugin-proposal-class-properties --save-dev .babelrc

Answer 16

对于弹出的 create-react-app 项目

我刚刚解决了我的案例，将以下几行添加到我的webpack.config.js：

  presets: [
    [
      require.resolve('babel-preset-react-app/dependencies'),
      { helpers: true },
    ],
    /* INSERT START */
    require.resolve('@babel/preset-env'),
    require.resolve('@babel/preset-react'),
      {
      'plugins': ['@babel/plugin-proposal-class-properties']
    } 
    /* INSERTED END */
  ],

Answer 17

如果有人在 react-native-web-monorepo 之后从事 monorepo 工作，那么您需要在 packages/web 中提交 config-overrides.js 文件。您需要在该文件中添加resolveApp('../../node_modules/react-native-ratings'),...

我完整的config-override.js 文件是

const fs = require('fs');
const path = require('path');
const webpack = require('webpack');

const appDirectory = fs.realpathSync(process.cwd());
const resolveApp = relativePath => path.resolve(appDirectory, relativePath);

// our packages that will now be included in the CRA build step
const appIncludes = [
    resolveApp('src'),
    resolveApp('../components/src'),
    resolveApp('../../node_modules/@react-navigation'),
    resolveApp('../../node_modules/react-navigation'),
    resolveApp('../../node_modules/react-native-gesture-handler'),
    resolveApp('../../node_modules/react-native-reanimated'),
    resolveApp('../../node_modules/react-native-screens'),
    resolveApp('../../node_modules/react-native-ratings'),
    resolveApp('../../node_modules/react-navigation-drawer'),
    resolveApp('../../node_modules/react-navigation-stack'),
    resolveApp('../../node_modules/react-navigation-tabs'),
    resolveApp('../../node_modules/react-native-elements'),
    resolveApp('../../node_modules/react-native-vector-icons'),
];

module.exports = function override(config, env) {
    // allow importing from outside of src folder
    config.resolve.plugins = config.resolve.plugins.filter(
        plugin => plugin.constructor.name !== 'ModuleScopePlugin'
    );
    config.module.rules[0].include = appIncludes;
    config.module.rules[1] = null;
    config.module.rules[2].oneOf[1].include = appIncludes;
    config.module.rules[2].oneOf[1].options.plugins = [
        require.resolve('babel-plugin-react-native-web'),
        require.resolve('@babel/plugin-proposal-class-properties'),
    ].concat(config.module.rules[2].oneOf[1].options.plugins);
    config.module.rules = config.module.rules.filter(Boolean);
    config.plugins.push(
        new webpack.DefinePlugin({ __DEV__: env !== 'production' })
    );

    return config
};

Answer 18

我在尝试使用 babel 转换一些 jsx 时遇到了同样的问题。以下是对我有用的解决方案。您可以将以下 json 添加到您的 .babelrc

{
  "presets": [
    [
      "@babel/preset-react",
      { "targets": { "browsers": ["last 3 versions", "safari >= 6"] } }
    ]
  ],
  "plugins": [["@babel/plugin-proposal-class-properties"]]
}

Answer 19

对于带有 webpack 的 react 项目：

1. 执行：npm install @babel/plugin-proposal-class-properties --save-dev
2. 在存在package.json 和webpack.config.js 的根文件夹中创建.babelrc（如果不存在）文件，并在其中添加以下代码：

{
  "presets": ["@babel/preset-env", "@babel/preset-react"],
  "plugins": [
    [
      "@babel/plugin-proposal-class-properties",
      {
        "loose": true
      }
    ]
  ]
}

1. 将以下代码添加到webpack.config.js 文件中：

{
            test: /\.jsx?$/,
            exclude: /node_modules/,
            loader: 'babel-loader',
            query: {
                presets: ["@babel/preset-env", "@babel/preset-react"]
            },
            resolve: {
                extensions: ['.js', '.jsx']
            }
}

4. 关闭终端并再次运行npm start。

Answer 20

您必须安装

npm install @babel/core @babel/plugin-proposal-class-properties @babel/preset-env @babel/preset-react babel-loader

和

更改输入和输出

---

const path = require('path')        
module.exports = {
  entry: path.resolve(__dirname,'src', 'app.js'),
  output: {
    path: path.resolve(__dirname, "public","dist",'javascript'),
    filename: 'bundle.js'
  },
  module: {
    rules: [
      {
        test: /\.(jsx|js)$/,
        exclude: /node_modules/,
        use: [{
          loader: 'babel-loader',
          options: {
            presets: [
              ['@babel/preset-env', {
                "targets": "defaults"
              }],
              '@babel/preset-react'
            ],
            plugins: [
              "@babel/plugin-proposal-class-properties"
            ]
          }
        }]
      }
    ]
  }
}

Answer 21

我为 src/components -> ../../components 创建了一个符号链接，导致 npm start 发疯并停止将 src/components/*.js 解释为 jsx，从而给出同样的错误。来自官方babel 的所有修复说明都是无用的。 当我复制回组件目录时，一切都恢复正常！

Answer 22

确保您没有错误地导入import BrowserRouter from "react-router-dom/modules/BrowserRouter"; 而不是import {BrowserRouter} from "react-router-dom";