由于@ babel / polyfill在7.4.0中已弃用，因此我试图直接添加core-js并通过corejs选项as decribed in the Babel documentation.设置版本。

但是，尝试这种方法时，我遇到了与polyfill相关的错误。 「（°ヘ°）

该应用可以编译，但是从不渲染-控制台记录错误"can't access lexical declaration `MEDIA_LARGE' before initialization"

我的webpack.config.js（Webpack 4.41.2）

'use strict'
const path = require('path')
const webpack = require('webpack')
const BundleAnalyzerPlugin = require('webpack-bundle-analyzer').BundleAnalyzerPlugin
const TerserPlugin = require('terser-webpack-plugin')
const MiniCssExtractPlugin = require('mini-css-extract-plugin')

process.env.NODE_ENV = process.env.NODE_ENV || 'development'
if (process.env.NODE_ENV === 'test') {
  require('dotenv').config({ path: '.env.test' })
} else if (process.env.NODE_ENV === 'development') {
  require('dotenv').config({ path: '.env.development' })
} else if (process.env.NODE_ENV === 'production') {
  require('dotenv').config({ path: '.env.production' })
} else {
  require('dotenv').config({ path: '.env.development' })
}

module.exports = (env) => {
  const isDev = env === 'development'
  const bundleName = 'bundle.js'

  const firebasePlugin = new webpack.DefinePlugin({
    'process.env.FIREBASE_API_KEY': JSON.stringify(process.env.FIREBASE_API_KEY),'process.env.FIREBASE_AUTH_DOMAIN': JSON.stringify(process.env.FIREBASE_AUTH_DOMAIN),'process.env.FIREBASE_DATABASE_URL': JSON.stringify(process.env.FIREBASE_DATABASE_URL),'process.env.FIREBASE_PROJECT_ID': JSON.stringify(process.env.FIREBASE_PROJECT_ID),'process.env.FIREBASE_STORAGE_BUCKET': JSON.stringify(process.env.FIREBASE_STORAGE_BUCKET),'process.env.FIREBASE_MESSAGING_SENDER_ID': JSON.stringify(process.env.FIREBASE_MESSAGING_SENDER_ID),'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),})

  const cssExtractPlugin = new MiniCssExtractPlugin({
    filename: '[name].css',chunkFilename: '[id].css',ignoreOrder: false
  })

  const plugins = isDev ? 
  [
    firebasePlugin,cssExtractPlugin,new BundleAnalyzerPlugin()
  ] 
  : 
  [
    firebasePlugin,new webpack.IgnorePlugin(/^\.\/locale$/,/moment$/),]

  // build WEBPACK CONFIG
  const config = {}

  config.devserver = {
    contentBase: path.join(__dirname,'public'),//absolute path
    historyApiFallback: true,publicPath: '/dist'
  }

  config.mode = env
  config.watch = isDev
  config.resolve = {
    extensions: ['.js','.jsx']
  }

  config.devtool = 'source-map'

  config.entry = ['./src/app.js']

  config.output = {
    path: path.join(__dirname,'public','dist'),//absolute path
    filename: bundleName
  }

  config.optimization = {
    minimize: true,minimizer: [
      new TerserPlugin({
        sourceMap: isDev,cache: true,parallel: true,terserOptions: {
          mangle: true,keep_classnames: true,keep_fnames: true,output: {
            comments: false
          }
        }
      })
    ]
  }
  config.plugins = plugins;
  config.module = {
    rules: [
    {
      test: /\.(js|jsx)$/,exclude: [
        /node_modules/,/firebase-functions/,/tests/
      ],use: {
        loader: 'babel-loader'
      }
    },{
      test: /\.svg$/,loader: 'svg-inline-loader'
    },{
      test: /\.s[ac]ss$/i,use: [
        'style-loader','css-loader','sass-loader',],},{
      test: /\.css$/,use: [
        {
          loader: MiniCssExtractPlugin.loader,options: {
            publicPath: '../',hmr: process.env.NODE_ENV === 'development',}
    ]
  }
  return config
}

我的babel.rc（Babel 7.7.2）

{
  "presets": [
    [
      "@babel/preset-env",{
        "targets": {
          "edge": "17","firefox": "60","chrome": "67","safari": "11.1"
        },"useBuiltIns": "usage","corejs": "3","debug": true
      }
    ],["@babel/preset-react"]
  ],"plugins": [
    "@babel/plugin-proposal-class-properties","@babel/plugin-proposal-object-rest-spread","emotion"
  ]
}

从Babel调试日志中，我可以看到正在使用polyfills

[C:\...\NotificationDateAlertList.js] Based on your code and targets,core-js polyfills were not added.

[C:\...\NotificationList.js] Added following core-js polyfill: es.array.sort { "safari":"11.1" }

[C:\...\commentactions.js] Added following core-js polyfill: es.promise { "edge":"17","firefox":"60" }

[C:\...\CommentListItem.js] Based on your code and targets,core-js polyfills were not added.

[C:\...\CommentForm.js] Added following core-js polyfill: es.string.match { "edge":"17" }

我已经确定了问题，但无法弄清楚为什么会收到错误消息。在下面的减速器中，我从操作中导入常量MEDIA_LARGE。

reducers / route.js

import { MEDIA_LARGE } from '../actions/routeactions'
const routeDefault = {
  page: '',prevPath: {},lastListPage: '',lastCatId: '',mediaSize: 'large'
}

const routeReducer = (state = routeDefault,action) => {
  //...
}

actions / routeactions.js ：export const MEDIA_LARGE = 'large'

替换常量导入有效，但是我怀疑这种行为还会破坏其他文件中的其他常量导入。 ：/

const routeDefault = {
  page: '',mediaSize: 'large'
}

为什么这行不通？我在这里做错什么了吗？

亲切的问候/ K