Webpack+Babel报错：'import'和'export'仅能在sourceType: module下使用

本人对Babel经验有限，运行JS应用时出现如下报错，若从webpack配置中移除"./src/index.js"，报错会消失但应用无法正常运行。

报错信息 #

ERROR in ./node_modules/@babel/runtime/regenerator/index.js 1:0
Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
File was processed with these loaders:
 * ./node_modules/babel-loader/lib/index.js
You may need an additional loader to handle the result of these loaders.
> import _typeof from "@babel/runtime/helpers/typeof";
| 
| // TODO(Babel 8): Remove this file.
 @ ./src/index.js 3:0-61 19:54-78 21:11-35 66:61-85 67:9-33

ERROR in   Error: Child compilation failed:
  Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  File was processed with these loaders:
   * ./node_modules/babel-loader/lib/index.js
  You may need an additional loader to handle the result of these loaders.
  > import _typeof from "@babel/runtime/helpers/typeof";
  | 
  | // TODO(Babel 8): Remove this file.:
  SyntaxError: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  ModuleParseError: Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  File was processed with these loaders:
   * ./node_modules/babel-loader/lib/index.js
  You may need an additional loader to handle the result of these loaders.
  > import _typeof from "@babel/runtime/helpers/typeof";
  | 
  | // TODO(Babel 8): Remove this file.
  
  - NormalModule.js:976 handleParseError
    [wolf3d-readyplayerme-threejs-boilerplate]/[webpack]/lib/NormalModule.js:976:19
  

ERROR in   Error: Child compilation failed:
  Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  File was processed with these loaders:
   * ./node_modules/babel-loader/lib/index.js
  You may need an additional loader to handle the result of these loaders.
  > import _typeof from "@babel/runtime/helpers/typeof";
  | 
  | // TODO(Babel 8): Remove this file.:
  SyntaxError: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  ModuleParseError: Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
  File was processed with these loaders:
   * ./node_modules/babel-loader/lib/index.js
  You may need an additional loader to handle the result of these loaders.
  > import _typeof from "@babel/runtime/helpers/typeof";
  | 
  | // TODO(Babel 8): Remove this file.
  
  - NormalModule.js:976 handleParseError
    [wolf3d-readyplayerme-threejs-boilerplate]/[webpack]/lib/NormalModule.js:976:19

  - child-compiler.js:131 
    [wolf3d-readyplayerme-threejs-boilerplate]/[html-webpack-plugin]/lib/child-compiler.js:131:18
  
  - Compiler.js:551 finalCallback
    [wolf3d-readyplayerme-threejs-boilerplate]/[webpack]/lib/Compiler.js:551:5
  

1 ERROR in child compilations (Use 'stats.children: true' resp. '--stats-children' for more details)
webpack 5.74.0 compiled with 4 errors and 11 warnings in 16857 ms

当前webpack.config.js配置 #

const webpack = require("webpack");
const path = require("path");
const CopyWebpackPlugin = require("copy-webpack-plugin");
const HtmlWebpackPlugin = require("html-webpack-plugin");

module.exports = (env) => {
  const isProd = env && env.prod;
  const config = {
    mode: isProd ? "production" : "development",
    performance: { hints: false },
    entry: ["babel-polyfill", "./src/index.js"],
    plugins: [
      new webpack.DefinePlugin({
        DEVELOPMENT: !isProd,
      }),
      new webpack.ProvidePlugin({
        process: 'process/browser',
      }),
      new HtmlWebpackPlugin({
        template: "./src/index.js",
      }),
      new CopyWebpackPlugin({
        patterns: [{ from: "src/assets", to: "assets" }],
      }),
      new HtmlWebpackPlugin({
        title: isProd ? "Production" : "Development",
        meta: {
          viewport:
            "width=device-width, initial-scale=1, shrink-to-fit=no, maximum-scale=1.0, user-scalable=no",
        },
      }),
    ],
    output: {
      filename: "[name].js",
      path: path.resolve(__dirname, "dist"),
    },
    resolve: {
      fallback: {
        util: require.resolve("util/")
      }
    },
    module: {
      rules: [
        {
          test: /\.(glsl|vs|fs|vert|frag)$/,
          use: ["raw-loader", "glslify-loader"],
        },
        {
          test: /\.js$/,
          use: {
            loader: "babel-loader",
            options: {
              compact: false,
              presets: [["@babel/preset-env"]],
              plugins: [
                ['@babel/plugin-transform-runtime', { "regenerator": true } ],
                "@babel/plugin-proposal-optional-chaining",
                "@babel/plugin-syntax-nullish-coalescing-operator",
              ],
            },
          },
        },
      ],
    },
  };

  if (!isProd) {
    config.devtool = "eval";
  }

  return config;
};

解决方案 #

1. 修复HtmlWebpackPlugin的错误配置 #

你重复实例化了HtmlWebpackPlugin，且第一个实例把JS文件(./src/index.js)作为template参数，这会导致插件试图将JS文件编译为HTML，触发额外的子编译流程，直接引发报错。

合并成一个正确的配置：

new HtmlWebpackPlugin({
  title: isProd ? "Production" : "Development",
  meta: {
    viewport: "width=device-width, initial-scale=1, shrink-to-fit=no, maximum-scale=1.0, user-scalable=no",
  },
  // 若需要自定义HTML结构，创建一个HTML模板文件（比如./src/index.html）并指定这里，不要用JS文件当模板
  // template: "./src/index.html"
}),

2. 让babel-loader处理@babel/runtime模块 #

默认情况下webpack不会处理node_modules下的文件，但@babel/runtime里的ES模块需要被转译。修改babel-loader规则，加入对@babel/runtime的处理：

{
  test: /\.js$/,
  // 包含src目录和@babel/runtime，确保这些文件被babel转译
  include: [path.resolve(__dirname, "src"), path.resolve(__dirname, "node_modules/@babel/runtime")],
  use: {
    loader: "babel-loader",
    options: {
      compact: false,
      presets: [["@babel/preset-env", {
        // 可选：根据目标浏览器配置，让babel更精准转译
        targets: "> 0.25%, not dead"
      }]],
      plugins: [
        ['@babel/plugin-transform-runtime', { "regenerator": true } ],
        "@babel/plugin-proposal-optional-chaining",
        "@babel/plugin-proposal-nullish-coalescing-operator" // 替换原有的syntax插件，proposal版本才能实际转译语法
      ],
    },
  },
},

3. 替换废弃的babel-polyfill #

babel-polyfill已被废弃，改用core-js和regenerator-runtime替代：

1. 先安装依赖：

npm install core-js@3 regenerator-runtime --save

2. 修改webpack的entry配置：

entry: ["core-js/stable", "regenerator-runtime/runtime", "./src/index.js"],

3. 同时在@babel/preset-env中配置相关选项：

presets: [["@babel/preset-env", {
  targets: "> 0.25%, not dead",
  useBuiltIns: "usage", // 自动按需引入polyfill
  corejs: 3 // 对应安装的core-js版本
}]],

内容的提问来源于stack exchange，提问作者v1rus96