背景

在 vue-cli3 发布之前，使用 vue-cli2 构建的 vue 项目是基于 webpack3.x 的，伴随着项目的版本迭代，功能逐渐增多，文件也逐渐增多，打包时间从最初的 4.5 分钟，最久的时候 17 分钟。

因为使用 ts 的缘故，每次打包 ts-loader 需要进行类型检查，导致耗时剧增。权衡利弊下，将 ts-loader 的类型检查禁用后（transpileOnly 选项设置为 true），打包时间锐减到 1 分钟。

随着时间的推移，项目依赖逐渐落后，打包时间也到了 2.5 分钟，恰逢 webpack4 对于打包性能的提升，于是就有了这篇升级日志：

起步

整体思路：

  1. 升级项目依赖
  2. 跑通开发环境打包
  3. 跑通生成环境打包

升级项目依赖

一开始的项目依赖升级的思路是，先升级 webpack 到最新的版本，然后逐步升级 loader 、plugin 、babel 等依赖。但是基于之前其他项目升级 webpack4 的经验，发现逐步升级会耗费一部分时间在新旧依赖的问题上，于是决定激进一点，使用 ncu 一次性将 package.json 中包含的项目依赖升级到最新版本，考虑到不确定性，可以选择性的修改 package.json 不升级某些依赖，比如主要版本号有变动的依赖（eg: 0.x.x => 1.x.x）。

# 安装 npm-check-updates
npm i -g npm-check-updates

# 检查项目依赖的版本与最新稳定版本，列出清单（beta版本可能不会列出来）
ncu

# 将 `package.json` 中包含的依赖的版本号，更新到最新
ncu -u

# 删除旧的依赖，安装新的依赖
rm -rf node_modules
rm package-lock.json
npm i

跑通开发环境打包

npm run dev

运行过程中遇到的问题：

  1. TypeError: proxyMiddleware is not a function

    报错日志：

    /Users/yourProjectPath/build/dev-server.js:47
  app.use(proxyMiddleware(options.filter || context, options));
        ^

TypeError: proxyMiddleware is not a function
    at /Users/yourProjectPath/build/dev-server.js:47:11
    at Array.forEach (<anonymous>)
    at Object.<anonymous> (/Users/yourProjectPath/build/dev-server.js:42:25)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Function.Module.runMain (module.js:684:10)
    at startup (bootstrap_node.js:187:16)
    at bootstrap_node.js:608:3

    原因：

    因为 http-proxy-middleware 升级到 v1.x 导致的：

    - "http-proxy-middleware": "~0.17.3",
+ "http-proxy-middleware": "~1.0.3",

    v1.x 起，需要通过主动导入 createProxyMiddleware 的方式使用中间件：

    // javascript

const express = require("express");
const { createProxyMiddleware } = require("http-proxy-middleware");

const app = express();

app.use(
  "/api",
  createProxyMiddleware({
    target: "http://www.example.org",
    changeOrigin: true,
  })
);
app.listen(3000);

// http://localhost:3000/api/foo/bar -> http://www.example.org/api/foo/bar

    如何解决：

    主动导入 createProxyMiddleware

    - const proxyMiddleware = require('http-proxy-middleware');
+ const { createProxyMiddleware } = require('http-proxy-middleware');

    将 proxyMiddleware 改为 createProxyMiddleware

    - app.use(proxyMiddleware(options.filter || context, options));
+ app.use(createProxyMiddleware(options.filter || context, options));

  2. vue-loader was used without the corresponding plugin. Make sure to include VueLoaderPlugin in your webpack config.

    vue-loader 如何从 v14 迁移至 v15

    报错日志：

    ERROR in ./src/App.vue
Module Error (from ./node_modules/vue-loader/lib/index.js):
vue-loader was used without the corresponding plugin. Make sure to include VueLoaderPlugin in your webpack config.
@ ./src/main.ts 2:0-28 45:23-26
@ multi ./build/dev-client ./src/main.ts

    ERROR in ./src/page/supplier/preferential/full-discount/view.vue?vue&type=script&lang=ts&
Module not found: Error: Can't resolve '../../../../interface/coupon.coupon_code_view' in '/Users/yourProjectPath/src/page/supplier/preferential/full-discount'
@ ./src/page/supplier/preferential/full-discount/view.vue?vue&type=script&lang=ts& 19:0-70
@ ./src/page/supplier/preferential/full-discount/view.vue
@ ./src/router/supplier/preferential.ts
@ ./src/router/supplier/index.ts
@ ./src/router/index.ts
@ ./src/main.ts
@ multi ./build/dev-client ./src/main.ts

    原因：

    vue-loader 升级到 v15.x 以后，需要搭配 VueLoaderPlugin 使用

    如何解决：

    // webpack.base.confg.js
const { VueLoaderPlugin } = require("vue-loader");

module.exports = {
  // ...
  plugins: [new VueLoaderPlugin()],
};

  3. Component template requires a root element, rather than just text.

    报错日志：

    Module Error (from ./node_modules/vue-loader/lib/loaders/templateLoader.js):
(Emitted value instead of an instance of Error)

Errors compiling template:

Component template requires a root element, rather than just text.

1   |
    |
2   |  #app
    |  ^^^^
3   |    router-view
    |  ^^^^^^^^^^^^^

 @ ./src/App.vue?vue&type=template&id=7ba5bd90&lang=pug& 1:0-238 1:0-238
 @ ./src/App.vue
 @ ./src/main.ts
 @ multi ./build/dev-client ./src/main.ts

    Module Error (from ./node_modules/vue-loader/lib/loaders/templateLoader.js):
(Emitted value instead of an instance of Error)

Errors compiling template:

text "div
el-card" outside root element will be ignored.

    原因：

    引用自 vue-loader 文档：

    注意有些模板的 loader 会导出一个编译好的模板函数而不是普通的 HTML，诸如 pug-loader。为了向 Vue 的模板编译器传递正确的内容，你必须换用一个输出普通 HTML 的 loader。例如，为了支持 <template lang="pug">，你可以使用 pug-plain-loader：

    如何解决：

    项目中使用到了 pug 语法，由于 vue-loader 的升级，现在需要引入 pug-plain-loader

    npm i -D pug-plain-loader

    // webpack.base.confg.js

module.exports = {
  // ...
  module: {
    rules: [
     // ...
      {
        test: /\.pug$/,
        loader: "pug-plain-loader"
      }
    ];
  }
};

  4. Cannot find module ‘@babel/core’

    报错日志：

    ERROR in ./src/store/mutation/util.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: Cannot find module '@babel/core'
babel-loader@8 requires Babel 7.x (the package '@babel/core'). If you'd like to use Babel 6.x ('babel-core'), you should install 'babel-loader@7'.
    at Function.Module._resolveFilename (module.js:538:15)
    at Function.Module._load (module.js:468:25)
    at Module.require (module.js:587:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/yourProjectPath/node_modules/babel-loader/lib/index.js:10:11)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Module.require (module.js:587:17)
    at require (internal/module.js:11:18)
    at loadLoader (/Users/yourProjectPath/node_modules/loader-runner/lib/loadLoader.js:18:17)
    at iteratePitchingLoaders (/Users/yourProjectPath/node_modules/loader-runner/lib/LoaderRunner.js:169:2)
    at runLoaders (/Users/yourProjectPath/node_modules/loader-runner/lib/LoaderRunner.js:365:2)
    at NormalModule.doBuild (/Users/yourProjectPath/node_modules/webpack/lib/NormalModule.js:295:3)
@ ./src/store/mutation/nav.ts 3:0-48 54:41-63 59:41-63 63:41-63 70:37-59
@ ./src/store/mutation/index.ts
@ ./src/store/index.ts
@ ./src/main.ts
@ multi ./build/dev-client ./src/main.ts

    原因：

    根据错误提示可以知道，babel-loader@8 依赖 Babel 7.x (也就是 @babel/core)。

    如何解决：

    卸载 babel-core

    npm un babel-core

    安装 @babel/core

    npm i -D @babel/core

  5. Cannot read property ‘bindings’ of null

    报错日志：

    Module build failed (from ./node_modules/babel-loader/lib/index.js):

TypeError: /Users/yourProjectPath/src/page/image-tag/bus.js: Cannot read property 'bindings' of null
at Scope.moveBindingTo (/Users/yourProjectPath/node_modules/@babel/traverse/lib/scope/index.js:926:13)
at BlockScoping.updateScopeInfo (/Users/yourProjectPath/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:364:17)
at BlockScoping.run (/Users/yourProjectPath/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:330:12)
at PluginPass.BlockStatementSwitchStatementProgram (/Users/yourProjectPath/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:70:24)
at newFn (/Users/yourProjectPath/node_modules/@babel/traverse/lib/visitors.js:179:21)
at NodePath.\_call (/Users/yourProjectPath/node_modules/@babel/traverse/lib/path/context.js:55:20)
at NodePath.call (/Users/yourProjectPath/node_modules/@babel/traverse/lib/path/context.js:42:17)
at NodePath.visit (/Users/yourProjectPath/node_modules/@babel/traverse/lib/path/context.js:90:31)
at TraversalContext.visitQueue (/Users/yourProjectPath/node_modules/@babel/traverse/lib/context.js:112:16)
at TraversalContext.visitSingle (/Users/yourProjectPath/node_modules/@babel/traverse/lib/context.js:84:19)
at TraversalContext.visit (/Users/yourProjectPath/node_modules/@babel/traverse/lib/context.js:140:19)
at Function.traverse.node (/Users/yourProjectPath/node_modules/@babel/traverse/lib/index.js:84:17)
at traverse (/Users/yourProjectPath/node_modules/@babel/traverse/lib/index.js:66:12)
at transformFile (/Users/yourProjectPath/node_modules/@babel/core/lib/transformation/index.js:107:29)
at transformFile.next (<anonymous>)
at run (/Users/yourProjectPath/node_modules/@babel/core/lib/transformation/index.js:35:12)

    原因：

    由于已经将 Babel 升级到 7.x，但是 .babelrc 仍在引用适用于 Babel 6.x 的 babel-preset-env

    如何解决：

    卸载 babel-preset-env

    npm un babel-preset-env

    安装 @babel/preset-env

    npm i -D @babel/preset-env

    从 .babelrc 中移除 babel-preset-env，改用 @babel/preset-env

    - { "presets": ["env"] }
+ { "presets": ["@babel/preset-env"] }

  6. this.setDynamic is not a function

    报错日志：

    ERROR in ./src/lib/image-drop.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
TypeError: /Users/yourProjectPath/src/lib/image-drop.js: this.setDynamic is not a function
    at PluginPass.pre (/Users/yourProjectPath/node_modules/babel-plugin-transform-runtime/lib/index.js:31:12)
    at transformFile (/Users/yourProjectPath/node_modules/@babel/core/lib/transformation/index.js:96:27)
    at transformFile.next (<anonymous>)
    at run (/Users/yourProjectPath/node_modules/@babel/core/lib/transformation/index.js:35:12)
    at run.next (<anonymous>)
    at Function.transform (/Users/yourProjectPath/node_modules/@babel/core/lib/transform.js:27:41)
    at transform.next (<anonymous>)
    at step (/Users/yourProjectPath/node_modules/gensync/index.js:254:32)
    at /Users/yourProjectPath/node_modules/gensync/index.js:266:13
    at async.call.result.err.err (/Users/yourProjectPath/node_modules/gensync/index.js:216:11)
    at /Users/yourProjectPath/node_modules/gensync/index.js:184:28
    at /Users/yourProjectPath/node_modules/@babel/core/lib/gensync-utils/async.js:72:7
    at /Users/yourProjectPath/node_modules/gensync/index.js:108:33
    at step (/Users/yourProjectPath/node_modules/gensync/index.js:280:14)
    at /Users/yourProjectPath/node_modules/gensync/index.js:266:13
    at async.call.result.err.err (/Users/yourProjectPath/node_modules/gensync/index.js:216:11)

    原因：

    由于已经将 Babel 升级到 7.x，但是 .babelrc 仍在引用适用于 Babel 6.x 的 babel-plugin-transform-runtime

    如何解决：

    卸载 babel-plugin-transform-runtime

    npm un babel-plugin-transform-runtime

    安装 @babel/plugin-transform-runtime

    npm i -D @babel/plugin-transform-runtime

    从 .babelrc 中移除 babel-preset-env，改用 @babel/plugin-transform-runtime

    - { "plugins": ["babel-plugin-transform-runtime"] }
+ { "plugins": ["@babel/plugin-transform-runtime"] }

  7. ValidationError: Invalid options object. CSS Loader has been initialized using an options object that does not match the API schema.

    报错日志：

    ERROR in ./node_modules/element-ui/lib/theme-chalk/index.css (./node_modules/css-loader/dist/cjs.js??ref--11-1!./node_modules/element-ui/lib/theme-chalk/index.css)
Module build failed (from ./node_modules/css-loader/dist/cjs.js):
ValidationError: Invalid options object. CSS Loader has been initialized using an options object that does not match the API schema.
- options has an unknown property 'minimize'. These properties are valid:
object { url?, import?, modules?, sourceMap?, importLoaders?, localsConvention?, onlyLocals? }
    at validate (/Users/yourProjectPath/node_modules/css-loader/node_modules/schema-utils/dist/validate.js:50:11)
    at Object.loader (/Users/yourProjectPath/node_modules/css-loader/dist/index.js:34:28)
@ ./node_modules/element-ui/lib/theme-chalk/index.css 4:14-81 14:3-18:5 15:22-89
@ ./src/main.ts
@ multi ./build/dev-client ./src/main.ts

    原因：

    minimize 配置项被移除导致

    如何解决：

    删除 css-loader 的 minimize 选项

  8. The ‘mode’ option has not been set

    报错日志：

    WARNING in configuration
The 'mode' option has not been set, webpack will fallback to 'production' for this value. Set 'mode' option to 'development' or 'production' to enable defaults for each environment.
You can also set it to 'none' to disable any default behavior. Learn more: https://webpack.js.org/configuration/mode/

    原因：

    webpack4 开始，提供了 mode 选项用来启用 webpack 提供的内置选项，没有设置时，默认值为 production

    如何解决：

    开发环境设置：development，生成环境设置：production

至此已经可以跑通开发环境打包了

跑通生成环境打包

运行过程中遇到的问题：

  1. webpack.optimize.CommonsChunkPlugin has been removed, please use config.optimization.splitChunks instead.

    报错日志：

    /Users/yourProjectPath/node_modules/webpack/lib/webpack.js:189
		throw new RemovedPluginError(errorMessage);
		^

Error: webpack.optimize.CommonsChunkPlugin has been removed, please use config.optimization.splitChunks instead.
    at Object.get [as CommonsChunkPlugin] (/Users/yourProjectPath/node_modules/webpack/lib/webpack.js:189:10)
    at Object.<anonymous> (/Users/yourProjectPath/build/webpack.prod.conf.js:85:26)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Module.require (module.js:587:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/yourProjectPath/build/build.js:12:23)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Function.Module.runMain (module.js:684:10)

    原因：

    https://webpack.js.org/migrate/4/#commonschunkplugin

    根据错误提示信息可以知道，webpack4 开始 CommonsChunkPlugin 被删除

    如何解决：

    将 CommonsChunkPlugin 相关的配置删除，改用 optimization.splitChunks 配置项

    The default configuration was chosen to fit web performance best practices, but the optimal strategy for your project might differ. If you’re changing the configuration, you should measure the impact of your changes to ensure there’s a real benefit. https://webpack.js.org/plugins/split-chunks-plugin/

    根据插件文档的描述，这里我们没有额外增加配置，使用的是 optimization.splitChunks 配置项的默认值。

    // webpack.config.js
module.exports = {
  // ...
  optimization: {
    splitChunks: {
      chunks: "async",
      minSize: 30000,
      maxSize: 0,
      minChunks: 1,
      maxAsyncRequests: 5,
      maxInitialRequests: 3,
      automaticNameDelimiter: "~",
      automaticNameMaxLength: 30,
      name: true,
      cacheGroups: {
        vendors: {
          test: /[\\/]node_modules[\\/]/,
          priority: -10,
        },
        default: {
          minChunks: 2,
          priority: -20,
          reuseExistingChunk: true,
        },
      },
    },
  },
};

  2. Error: Chunk.entrypoints: Use Chunks.groupsIterable and filter by instanceof Entrypoint instead

    报错日志：

    /Users/yourProjectPath/node_modules/webpack/lib/Chunk.js:866
	throw new Error(
	^

Error: Chunk.entrypoints: Use Chunks.groupsIterable and filter by instanceof Entrypoint instead
    at Chunk.get (/Users/yourProjectPath/node_modules/webpack/lib/Chunk.js:866:9)
    at /Users/yourProjectPath/node_modules/extract-text-webpack-plugin/dist/index.js:176:48
    at Array.forEach (<anonymous>)
    at /Users/yourProjectPath/node_modules/extract-text-webpack-plugin/dist/index.js:171:18
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/yourProjectPath/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:7:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/yourProjectPath/node_modules/tapable/lib/Hook.js:154:20)
    at Compilation.seal (/Users/yourProjectPath/node_modules/webpack/lib/Compilation.js:1342:27)
    at compilation.finish.err (/Users/yourProjectPath/node_modules/webpack/lib/Compiler.js:675:18)
    at hooks.finishModules.callAsync.err (/Users/yourProjectPath/node_modules/webpack/lib/Compilation.js:1261:4)
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/yourProjectPath/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:24:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/yourProjectPath/node_modules/tapable/lib/Hook.js:154:20)
    at Compilation.finish (/Users/yourProjectPath/node_modules/webpack/lib/Compilation.js:1253:28)
    at hooks.make.callAsync.err (/Users/yourProjectPath/node_modules/webpack/lib/Compiler.js:672:17)
    at _done (eval at create (/Users/yourProjectPath/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:9:1)
    at _err1 (eval at create (/Users/yourProjectPath/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:32:22)
    at _addModuleChain (/Users/yourProjectPath/node_modules/webpack/lib/Compilation.js:1185:12)

    原因：

    extract-text-webpack-plugin 在 webpack4 的时候被废弃，改用mini-css-extract-plugin

    如何解决：

    卸载 extract-text-webpack-plugin

    npm un extract-text-webpack-plugin

    安装 mini-css-extract-plugin

    npm i -D mini-css-extract-plugin

    将 extract-text-webpack-plugin 相关的配置删除，改用 mini-css-extract-plugin

    // utils.js
-const ExtractTextPlugin = require('extract-text-webpack-plugin');
+const MiniCssExtractPlugin = require('mini-css-extract-plugin');

if (options.extract) {
-  return ExtractTextPlugin.extract({
-    use: loaders,
-    fallback: 'vue-style-loader'
-  });
+  return [
+    {
+      loader: MiniCssExtractPlugin.loader,
+      options: {
+        hmr: process.env.NODE_ENV === 'development'
+      }
+    }
+  ].concat(loaders);
} else {
  return ['vue-style-loader'].concat(loaders);
}

    // webpack.prod.conf.js
-const ExtractTextPlugin = require('extract-text-webpack-plugin');
+const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  // ...
  plugins: [
-   new ExtractTextPlugin({
+   new MiniCssExtractPlugin({
      filename: utils.assetsPath('css/[name].[contenthash].css'),
    }),
  ]
}

    如果不是使用 vue-cli 2.x 搭建的项目，可能需要这样修改：

    详情见：https://webpack.js.org/plugins/mini-css-extract-plugin/

    // webpack.prod.conf.js
// ***
const MiniCssExtractPlugin = require("mini-css-extract-plugin");

module.exports = {
  module: {
    rules: [
      // ***
      {
        test: /\.css$/,
        use: [
          {
            loader: MiniCssExtractPlugin.loader,
            options: {
              hmr: process.env.NODE_ENV === "development",
            },
          },
          "css-loader",
        ],
      },
    ],
  },
  plugins: [
    // ***
    new MiniCssExtractPlugin({
      filename: "[name].[contenthash].css",
    }),
  ],
};

  3. DefaultsError: warnings is not a supported option

    报错日志：

    ERROR in static/js/170.b2935281265dd9ec23b7.js from UglifyJs

DefaultsError: `warnings` is not a supported option
at DefaultsError.get (eval at <anonymous> (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/node_modules/uglify-js/tools/node.js:18:1), <anonymous>:71:23)
at Function.buildError (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/index.js:105:54)
at results.forEach (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/index.js:258:52)
at Array.forEach (<anonymous>)
at taskRunner.run (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/index.js:233:17)
at step (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:85:9)
at done (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:96:30)
at boundWorkers (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:101:13)
at TaskRunner.boundWorkers (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:70:11)
at enqueue (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:91:14)
at tasks.forEach (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:111:9)
at Array.forEach (<anonymous>)
at TaskRunner.run (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/TaskRunner.js:89:11)
at UglifyJsPlugin.optimizeFn (/Users/yourProjectPath/node_modules/uglifyjs-webpack-plugin/dist/index.js:227:18)
at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/yourProjectPath/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:31:1)
at AsyncSeriesHook.lazyCompileHook (/Users/yourProjectPath/node_modules/tapable/lib/Hook.js:154:20)

    原因：

    由于 UglifyJs 升级导致的，uglifyjs-webpack-plugin 依赖于 UglifyJs

    详情见：https://github.com/mishoo/UglifyJS2/issues/3394

    如何解决：

    将 uglifyOptions.compress 选项删除

    // webpack.prod.conf.js
new UglifyJsPlugin({
  uglifyOptions: {
-   compress: {
      warnings: false,
      drop_console: true,
      drop_debugger: true
-   }
  }
}),

  4. Unexpected token: keyword «const»

    报错日志：

    ERROR in static/js/app.2c7ff4a31971e22c9397.js from UglifyJs
Unexpected token: keyword «const» [static/js/app.2c7ff4a31971e22c9397.js:3865,0]

    原因：

    uglifyjs-webpack-plugin 不支持 es6 语法

    如何解决：

    卸载 uglifyjs-webpack-plugin

    npm un uglifyjs-webpack-plugin

    将 uglifyjs-webpack-plugin 相关的配置删除，不用额外增加配置，因为 production 模式下，webpack 默认使用 terser-webpack-plugin 来最小化 JavaScript 文件

总结

至此经历了一系列的各种问题之后，开发和生产环境打包都已经可以跑通了。这篇文章记录了的两个 webpack 3.x 项目升级到 webpack 4.x 时遇到的问题、原因和解决方法，希望对你们有帮助。

升级后生产环境打包速度有所提升，但是文件大小并不理想，下一篇我会讲如何对 webpack 的打包进行优化。

参考链接