获取全套webpack 4.x教程，请访问瓦力博客

在上一小节，我们将开发环境和生产环境区分开来。这一小节，我们来操作如何将样式文件的代码分割。

1.安装

yarn add mini-css-extract-plugin

此插件将CSS提取到单独的文件中。它为每个包含CSS的JS文件创建一个CSS文件。它支持CSS和SourceMaps的按需加载。

它建立在新的webpack v4功能(模块类型)之上，并且需要webpack 4才能工作。

注意:MiniCssExtractPlugin 目前不支持HMR support(热重载)

2.提取css

bulid/plugins.js

const srcPath = require('./base/path');

const config = require('./base/config');

const webpack = require('webpack');

const HtmlWebpackPlugin = require('html-webpack-plugin'); //生成html文件

const { CleanWebpackPlugin } = require('clean-webpack-plugin'); //清除

+ const MiniCssExtractPlugin = require("mini-css-extract-plugin"); //css样式提取

let plugins = [

new HtmlWebpackPlugin({

title: '瓦力博客',

template: srcPath.src + '/index.html' //以src/index.html为编译模板

}),

+new MiniCssExtractPlugin({

+filename: config.NODE_ENV == 'development'?'[name.css]': `${srcPath.css}/[name].[hash].css`,

+chunkFilename: config.NODE_ENV == 'development'?'[id].css': `${srcPath.css}/[id].[hash].css`

+}), //css提取

new CleanWebpackPlugin(),

new webpack.HotModuleReplacementPlugin()

]

module.exports = plugins;

build/module.js

const srcPath = require('./base/path');

const config = require('./base/config');

+ const MiniCssExtractPlugin = require("mini-css-extract-plugin");

let _module = {

rules:[

{

test:/\.css$/,

use:[

+config.NODE_ENV == 'development'?'style-loader': MiniCssExtractPlugin.loader,

{

loader:'css-loader',

options:{

importLoaders:1

}

},

'postcss-loader'

]

},

{

test:/\.scss$/,

use:[

+config.NODE_ENV == 'development'?'style-loader': MiniCssExtractPlugin.loader,

{

loader:'css-loader',

options:{

importLoaders:2

}

},

'sass-loader',

'postcss-loader'

]

},

{

test: /\.less$/,

use: [

+config.NODE_ENV == 'development'?'style-loader': MiniCssExtractPlugin.loader,

{

loader:'css-loader',

options:{

importLoaders:2

}

},

'less-loader',

'postcss-loader'

]

},

{

test:/\.(png|svg|jpeg|jpg|gif)$/,

use:[

{

loader:'file-loader',

options:{

name:'[name][sha512:hash:base64:7].[ext]', //[path] 上下文环境路径

outputPath: srcPath.images, //输出路径

publicPath: config.NODE_ENV === 'development'?srcPath.images:srcPath.images //公共路径

}

},

{

loader: 'image-webpack-loader',

options: {

bypassOnDebug: true, // webpack@1.x

disable: true, // webpack@2.x and newer

},

},

]

},

{

test: /\.html$/,

use:[

{

loader:'html-loader',

options:{

arrts:['img:src','img:data-src'],

+minimize:config.NODE_ENV === 'development'? false:false //是否压缩html

}

}

]

},

{

test: /(iconfont.svg)|\.(woff|woff2|eot|ttf|otf)$/,

use:[

{

loader:'file-loader',

options:{

name:'[name].[ext]', //[path] 上下文环境路径

outputPath: srcPath.iconfont, //输出路径

publicPath: config.NODE_ENV === 'development'? srcPath.iconfont: srcPath.iconfont, //公共路径

}

}

]

},

{

test: /\.js$/,

exclude: /(node_modules|bower_components|lib)/,

loader: 'babel-loader'

}

]

}

module.exports = _module;

build/base/config.js

let _mode = process.argv[process.argv.length - 1];

let env = _mode.replace(/--mode=(.+)/g,"$1");

let config = {

NODE_ENV: env == 'development'?'development':'production', //development 开发 production 线上

+publicPath: env == 'development'?'./':'./',

apiUrl:'http://www.waliblog.com',

port: 9999

}

module.exports = config;

package.json

{

"name": "webpack",

"version": "1.0.0",

"description": "webpack测试",

"sideEffects": [

"*.css",

+"*.less",

+"*.scss"

],

"main": "index.js",

"author": "wali",

"private": true,

"license": "MIT",

"scripts": {

"dev": "npx webpack-dev-server --colors --mode=development",

"prod": "npx webpack --colors --mode=production",

"build": "npx webpack --colors --mode=development",

"analyse": "npx webpack --profile --json> stats.json --colors --mode=development"

},

"dependencies": {

"@babel/core": "^7.4.5",

"@babel/plugin-syntax-dynamic-import": "^7.2.0",

"@babel/plugin-transform-runtime": "^7.4.4",

"@babel/polyfill": "^7.4.4",

"@babel/preset-env": "^7.4.5",

"@babel/runtime": "^7.4.5",

"@babel/runtime-corejs2": "^7.4.5",

"autoprefixer": "^9.5.1",

"babel-loader": "^8.0.6",

"clean-webpack-plugin": "^3.0.0",

"css-loader": "^2.1.1",

"extract-text-webpack-plugin": "^3.0.2",

"file-loader": "^3.0.1",

"html-loader": "^0.5.5",

"html-webpack-plugin": "^3.2.0",

"image-webpack-loader": "^4.6.0",

"json5-loader": "^2.0.0",

"less": "^3.9.0",

"less-loader": "^5.0.0",

"loadsh": "^0.0.4",

"lodash": "^4.17.11",

"mini-css-extract-plugin": "^0.7.0",

"node-sass": "^4.12.0",

"postcss-loader": "^3.0.0",

"sass-loader": "^7.1.0",

"style-loader": "^0.23.1",

"webpack": "^4.32.0",

"webpack-cli": "^3.3.2",

"webpack-dev-server": "^3.4.1"

},

"devDependencies": {

"webpack-bundle-analyzer": "^3.3.2"

}

}

index.js

import './assets/css/index.css';

assets/css/index.css

h1{

color: blue;

}

运行webpack

yarn run prod

打开dist/index.html,看到/assets/css/index.css文件样式生效了

title

欢迎来到瓦力博客

从index.html文件中可以看到css文件被提取出来，并且被引用。

3.提取sass

上面配置已经写了，在plugins.js和module.js文件中配置了，这里就简单的验证一下

修改index.js

import './assets/sass/index.scss';

assets/sass/index.scss

body{

h1{

transform: translate(100px, 100px);

}

}

运行webpack

yarn run prod

打开dist/index.html发现欢迎来到瓦力博客几个字发生偏移，说明/assets/sass/index.scss样式已经生效

4.提取less

上面配置已经写了，在plugins.js和module.js文件中配置了，这里就简单的验证一下

修改index.js

import './assets/less/index.less';

assets/less/index.less

body{

h1{

transform: rotate(90deg);

background: red;

text-align: center;

}

}

运行webpack

yarn run prod

打开dist/index.html发现欢迎来到瓦力博客几个字旋转90度，背景变红，字体居中，说明/assets/less/index.less样式已经生效

5.生产环境css压缩

安装optimize-css-assets-webpack-plugin

yarn add optimize-css-assets-webpack-plugin

optimization.js

+ const config = require('./base/config');

+ const OptimizeCssAssetsPlugin = require('optimize-css-assets-webpack-plugin');

let optimization = {

usedExports: true,

splitChunks: {

chunks: 'all',

minSize: 30000,

maxSize: 0,

minChunks: 1,

maxAsyncRequests: 5,

maxInitialRequests: 3,

automaticNameDelimiter: '~',

name: true,

cacheGroups: {

vendors: {

test: /[\\/]node_modules[\\/]/,

priority: -10

},

default: {

minChunks: 2,

priority: -20,

reuseExistingChunk: true

}

}

}

}

+if(config.NODE_ENV != 'development'){

+optimization['minimizer'] = [new OptimizeCssAssetsPlugin({})]

+}

module.exports = optimization

运行开发环境

yarn run build

发现没有发生什么改变，样式都在head标签内

运行生产环境

yarn run prod

发现dist目录下有css目录生成，打开css文件，看到css被压缩了。

6.总结

测试这小节其实遇到几个问题，小菜写出来：

调试

这小节的测试命令都变成yarn run prod，是测试生产环境下webpack配置，生产环境下css,less,scss都会被压缩，去注释，index.html文件也会被压缩，去注释，还要添加域名。这样一来从生成的文件方面就不容易看出webpack到底是否配置正确。所以小菜将config.js中修改

+publicPath: env == 'development'?'./':'./',

就是生成后index.html文件能直接在本地打开而不报错。

build/module.js修改

+minimize:config.NODE_ENV === 'development'? false:false //是否压缩html

生成后index.html文件不要被压缩，还保留树形结构，便于查找

less和scss文件样式不起作用

小菜起初测试css文件，发现打包后css样式被提取出来，样式也生效了，但是换成

import './assets/less/index.less';

//或

import './assets/sass/index.scss';

时，在运行打包命令时，样式没有被提取出来。后来经过认真分析，发现/webpack/2019/05/24/webpack-10.html一节中配置了Tree Shaking。Tree shaking作用就是当我在index.js文件中使用import './assets/less/index.less'写法时，会检测在js文件中是否使用了引入来的less，很明显在index.js文件中没有使用，只是单纯的引入，所以Tree shaking就会自动帮我们过滤掉这行代码，就导致最终生成的js文件中没有样式，也就提取不出来样式了。

看了上面的解释，有的小伙伴可能会问import './assets/css/index.css'也在index.js文件中只引用没有使用，为什么css文件中的样式就能够生效呢？原因还是在/webpack/2019/05/24/webpack-10.html一节中，小菜在package.json中配置了css，没有配置less,scss。

"sideEffects": [

"*.css",

+"*.less",

+"*.scss"

],

当我们配置*.css,*.less,*.scss后，在Tree shaking时，webpack就会知道忽略css,less,scss所有文件，即使在js文件中css,less,scss只引用没有使用，也不要删除这行代码。

7.代码回滚

build/module.js

- minimize:config.NODE_ENV === 'development'? false:false //是否压缩html

+ minimize:config.NODE_ENV === 'development'? false:true //是否压缩html

build/base/config.js

let _mode = process.argv[process.argv.length - 1];

let env = _mode.replace(/--mode=(.+)/g,"$1");

let config = {

NODE_ENV: env == 'development'?'development':'production', //development 开发 production 线上

-publicPath: env == 'development'?'./':'./',

+publicPath: env == 'development'?'./':'http://www.waliblog.com/',

apiUrl:'http://www.waliblog.com',

port: 9999

}

module.exports = config;