Webpack常见静态资源处理-模块加载器（Loaders）+ExtractTextPlugin插件

2019-11-19 16:13:11

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webpack系列目录

webpack 系列二：webpack 介绍&安装

webpack 系列三：webpack 如何集成第三方js库

webpack 系列四：webpack 多页面支持 & 公共组件单独打包

webpack 系列五：webpack Loaders 模块加载器

webpack 系列六：前端项目模板-webpack+gulp实现自动构建部署

基于webpack搭建纯静态页面型前端工程解决方案模板，最终形态源码见github: https://github.com/ifengkou/webpack-template

正文

Webpack将所有静态资源都认为是模块，比如JavaScript，CSS，LESS，TypeScript，JSX，CoffeeScript，图片等等，从而可以对其进行统一管理。为此Webpack引入了加载器的概念，除了纯JavaScript之外，每一种资源都可以通过对应的加载器处理成模块。和大多数包管理器不一样的是，Webpack的加载器之间可以进行串联，一个加载器的输出可以成为另一个加载器的输入。比如LESS文件先通过less-load处理成css，然后再通过css-loader加载成css模块，最后由style-loader加载器对其做最后的处理，从而运行时可以通过style标签将其应用到最终的浏览器环境。

一常用loader

安装css/sass/less loader加载器

复制代码代码如下:

cnpm install file-loader css-loader style-loader sass-loader ejs-loader html-loader jsx-loader image-webpack-loader --save-dev

webpack.config.js配置：

module: { loaders: [  {   test: //.((woff2?|svg)(/?v=[0-9]/.[0-9]/.[0-9]))|(woff2?|svg|jpe?g|png|gif|ico)$/,   loaders: [    // 小于10KB的图片会自动转成dataUrl    'url?limit=10240&name=img/[hash:8].[name].[ext]',    'image?{bypassOnDebug:true, progressive:true,optimizationLevel:3,pngquant:{quality:"65-80",speed:4}}'   ]  },  {   test: //.((ttf|eot)(/?v=[0-9]/.[0-9]/.[0-9]))|(ttf|eot)$/,   loader: 'url?limit=10000&name=fonts/[hash:8].[name].[ext]'  },  {test: //.(tpl|ejs)$/, loader: 'ejs'},  {test: //.css$/, loader: 'style-loader!css-loader'},  { test: //.scss$/, loader: 'style!css!sass'} ]},

index.html 新增两个div

<div class="small-webpack"></div><div class="webpack"></div>

index.css 增加两个图片，同时将webpack.png（53kb) 和 small-webpack.png(9.8k)

.webpack { background: url(../img/webpack.png) no-repeat center; height:500px;}.small-webpack { background: url(../img/small-webpack.png) no-repeat center; height:250px;}

index.js 引入css

require('../css/index.css');

执行webpack指令

$ webpack

查看生成的目录结构

其中并没有css文件，css被写入到了index.js中，index.js 部分截图

总结：

图片采用了url-loader加载，如果小于10kb，图片则被转化成 base64 格式的 dataUrl

css文件被打包进了js文件中

css被打包进了js文件，如果接受不了，可以强制把css从js文件中独立出来。官方文档是以插件形式实现：文档docs点这，插件的github点这

二：extract-text-webpack-plugin 插件介绍

Extract text from bundle into a file.从bundle中提取出特定的text到一个文件中。使用 extract-text-webpack-plugin就可以把css从js中独立抽离出来

安装

$ npm install extract-text-webpack-plugin --save-dev

使用（css为例）

var ExtractTextPlugin = require("extract-text-webpack-plugin");module.exports = { module: {  loaders: [   { test: //.css$/, loader: ExtractTextPlugin.extract("style-loader", "css-loader") }  ] }, plugins: [  new ExtractTextPlugin("styles.css") ]}

它将从每一个用到了require("style.css")的entry chunks文件中抽离出css到单独的output文件

API

new ExtractTextPlugin([id: string], filename: string, [options])

id Unique ident for this plugin instance. (For advanded usage only, by default automatic generated)
filename the filename of the result file. May contain [name], [id] and [contenthash].
1. [name] the name of the chunk
2. [id] the number of the chunk
3. [contenthash] a hash of the content of the extracted file
options
1. allChunks extract fromall additional chunks too (by default it extracts only from the initial chunk(s))
2. disable disables the plugin

ExtractTextPlugin.extract([notExtractLoader], loader, [options])

根据已有的loader，创建一个提取器（loader的再封装）

notExtractLoader （可选）当css没有被抽离时，加载器不应该使用（例如：当allChunks:false时，在一个additional 的chunk中）
loader 数组，用来转换css资源的加载器s
options
1. publicPath 重写该加载器(loader)的 publicPath 的设置

多入口文件的extract的使用示例：

let ExtractTextPlugin = require('extract-text-webpack-plugin');// multiple extract instanceslet extractCSS = new ExtractTextPlugin('stylesheets/[name].css');let extractLESS = new ExtractTextPlugin('stylesheets/[name].less');module.exports = { ... module: { loaders: [  {test: //.scss$/i, loader: extractCSS.extract(['css','sass'])},  {test: //.less$/i, loader: extractLESS.extract(['css','less'])},  ... ] }, plugins: [ extractCSS, extractLESS ]};

三：改造项目-抽离css

安装插件到项目

npm install extract-text-webpack-plugin --save-dev

配置webpack.config.js，加入ExtractTextPlugin和相关处理：

var webpack = require("webpack");var path = require("path");var srcDir = path.resolve(process.cwd(), 'src');var nodeModPath = path.resolve(__dirname, './node_modules');var pathMap = require('./src/pathmap.json');var glob = require('glob')var CommonsChunkPlugin = webpack.optimize.CommonsChunkPlugin;var HtmlWebpackPlugin = require('html-webpack-plugin');var ExtractTextPlugin = require('extract-text-webpack-plugin');var entries = function () { var jsDir = path.resolve(srcDir, 'js') var entryFiles = glob.sync(jsDir + '/*.{js,jsx}') var map = {}; for (var i = 0; i < entryFiles.length; i++) {  var filePath = entryFiles[i];  var filename = filePath.substring(filePath.lastIndexOf('//') + 1, filePath.lastIndexOf('.'));  map[filename] = filePath; } return map;}var html_plugins = function () { var entryHtml = glob.sync(srcDir + '/*.html') var r = [] var entriesFiles = entries() for (var i = 0; i < entryHtml.length; i++) {  var filePath = entryHtml[i];  var filename = filePath.substring(filePath.lastIndexOf('//') + 1, filePath.lastIndexOf('.'));  var conf = {   template: 'html!' + filePath,   filename: filename + '.html'  }  //如果和入口js文件同名  if (filename in entriesFiles) {   conf.inject = 'body'   conf.chunks = ['vendor', filename]  }  //跨页面引用，如pageA,pageB 共同引用了common-a-b.js，那么可以在这单独处理  //if(pageA|pageB.test(filename)) conf.chunks.splice(1,0,'common-a-b')  r.push(new HtmlWebpackPlugin(conf)) } return r}var plugins = [];var extractCSS = new ExtractTextPlugin('css/[name].css?[contenthash]')var cssLoader = extractCSS.extract(['css'])var sassLoader = extractCSS.extract(['css', 'sass'])plugins.push(extractCSS);plugins.push(new CommonsChunkPlugin({ name: 'vendor', minChunks: Infinity}));module.exports = { entry: Object.assign(entries(), {  // 用到什么公共lib（例如jquery.js），就把它加进vendor去，目的是将公用库单独提取打包  'vendor': ['jquery', 'avalon'] }), output: {  path: path.join(__dirname, "dist"),  filename: "[name].js",  chunkFilename: '[chunkhash:8].chunk.js',  publicPath: "/" }, module: {  loaders: [   {    test: //.((woff2?|svg)(/?v=[0-9]/.[0-9]/.[0-9]))|(woff2?|svg|jpe?g|png|gif|ico)$/,    loaders: [     //小于10KB的图片会自动转成dataUrl，     'url?limit=10000&name=img/[hash:8].[name].[ext]',     'image?{bypassOnDebug:true, progressive:true,optimizationLevel:3,pngquant:{quality:"65-80",speed:4}}'    ]   },   {    test: //.((ttf|eot)(/?v=[0-9]/.[0-9]/.[0-9]))|(ttf|eot)$/,    loader: 'url?limit=10000&name=fonts/[hash:8].[name].[ext]'   },   {test: //.(tpl|ejs)$/, loader: 'ejs'},   {test: //.css$/, loader: cssLoader},   {test: //.scss$/, loader: sassLoader}  ] }, resolve: {  extensions: ['', '.js', '.css', '.scss', '.tpl', '.png', '.jpg'],  root: [srcDir, nodeModPath],  alias: pathMap,  publicPath: '/' }, plugins: plugins.concat(html_plugins())}

其中，用ExtractTextPlugin 来抽离css

var ExtractTextPlugin = require('extract-text-webpack-plugin');var extractCSS = new ExtractTextPlugin('css/[name].css?[contenthash]')var cssLoader = extractCSS.extract(['css'])var sassLoader = extractCSS.extract(['css', 'sass'])plugins.push(extractCSS);......//conf - module - loaders{test: //.css$/, loader: cssLoader},{test: //.scss$/, loader: sassLoader}

注意事项：

css中img的路径会出现问题，通过设置publicPath 解决，采用绝对路径