webpack3.x migration and upgrade

This time I will bring you webpack3.x migration and upgrade. What are the precautions for webpack3.x migration and upgrade? The following is a practical case, let’s take a look.

Digression: Don’t look at the 0 configuration as it is very gimmick. It basically cannot meet the needs of most users. However, adding more default configurations does make it more convenient for users. The configuration is relatively simple and is a kind of Out of the box way. After all, the 0 configuration of parcel did steal a lot of the limelight of webpack before, and then I also worked on a simple template project of parcel using parcel vue. If you are interested, you can take a look.

1. New things in webpack4

0. Installation

is no longer just installationwebpack is enough, you also need to install a webpack-cli:

Global installation

sudo npm install -g webpack webpack-cli

Partial installation (current folder)

npm install --save-dev webpack webpack-cli

1. 0 configuration

The default entry is './src/' and the default exit './dist';

The setting of compression (optimization.minimize) is turned on by default during production and turned off during development.

The default configuration is not limited to the above two items.

2. mode/–mode parameter

The mode/--mode parameter is added to indicate whether it is development or production. mode has two optional values: development And production, production does not support monitoring, production focuses on the packaged file size, and development focuses on the speed of the build.

webpack --mode development

can also be configured in the configuration file:

// webpack.config.js
module.exports = {
 mode: "production",
 // ...
}

3. Upgrade uglifyjs

The webpack-based project created by the previous vue scaffolding , in webpack.prod.conf.js you can clearly see this line in the configuration:

// UglifyJs do not support ES6, you can also use babel- minify for better treeshaking: https://github.com/babel/minify

In webpack4.0, es6 code can already be compressed, such as:

class user {
 getUsername() {
  // to do
 }
}

After compression:

4. To remove loaders, you must use rules

In webpack3.x, the loaders of the previous version are still retained and coexist with the rules. All can be used. Loaders have been completely removed in the new version, and rules must be used.

5. sideEffects

Add sideEffects:false in the module's package.js. When using export to export separately, other files other than export will not be packaged. , making the packaged file smaller.

Related links: https://github.com/webpack/webpack/tree/master/examples/side-effects

6. webpack4 supports multiple forms of module types, But sometimes you may need to add type for coordination

If it is CommonJS, AMD, ESM three types of modules, use javascript/auto;

If it is EcmaScript modules(.mjs ), use javascript/esm, other module types will not take effect;

If only CommonJS and EcmaScript modules are not available, use javascript/dynamic;

If it is a json type file, it is allowed to be used To import json with require and import, use json;

If it is Webassembly, use webassembly/experimental - it is officially an experimental feature.

For example:

rules: [
 {
  test: /\.json$/,
  type: "javascript/auto"
 }
]

7. Supports ES6 import of JSON files, and can filter useless code

The following are three imports Method of json file:

let jsonData = require('./data.json');
import jsonData from './data.json'
import { first } from './data.json'

The json file introduced using import { first } from './data.json' will ignore the unimported code, and only the first one will be included when packaging.

8. Remove CommonsChunkPlugin and replace it with optimization.splitChunks and optimization.runtimeChunk

There is a lot of content here, so I won’t give a detailed introduction. There may be a follow-up article Articles about optimization.splitChunks will be briefly introduced below when migrating from 3.x. In addition to the new version of relesase link above, here are some good links recommended:

RIP CommonsChunkPlugin
Article about removing CommonsChunkPlugin on medium
Article about webpack4 update on medium

二、webpack 3.X 迁移到 webpack4.X

1. 更新webpack依赖

npm install -g webpack webpack-cli
npm install --save-dev webpack webpack-cli

2. 更新对应模块

在webpack升级的同时，对应的许多依赖也需要相应的进行升级，下面是在vuec-cli的脚手架中需要的更新；对于其他工程，注意看控制台的报错，是哪个插件报的错就去升级那个插件，如果存在找不到模块之类的错误就去升级对应的loader。

html-webpack-plugin => npm i -D html-webpacl-plugin

webpack-dev-server或者改为webpack-serve => npm i -D webpack-dev-server/npm i -D webpack-serve

vue-loader => npm i -D vue-loader

extract-text-webpack-plugin@next => npm i -D extract-text-webpack-plugin@next <br>…

3. 使用mode/–mode

在命令中加入--mode development/ --mode production或者在配置文件中加入mode: 'development'/mode: 'production'。

4. 如果使用CommonsChunkPlugin替换为optimization.splitChunks

使用栗子：

const webpack = require('webpack')；
new webpack.optimize.SplitChunksPlugin({
 chunks: "all",
 minSize: 30000,
 minChunks: 1,
 maxAsyncRequests: 5,
 maxInitialRequests: 3,
 name: true,
 cacheGroups: {
  default: {
   minChunks: 2,
   priority: -20,
   reuseExistingChunk: true,
  },
  vendors: {
   test: /[\\/]node_modules[\\/]/,
   priority: -10
  }
 }
})

写在后面

对于webpack的这次升级这里没有一一列举，选了几个相对关键的点，具体可以去看这里；有关从webpack3.x迁移到新版的时候可能还有其他的坑需要慢慢去趟，目前遇到的基本都解决了。

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