详解Web如何使用webpack构建前端项目

好久没写技术博客了, 原因在于最近在学习前端方面的技术, 熟悉我的同学都知道, 之前我有使用Vue搭建了一个个人简历, 体验了一把最新的前端技术, 但之前我们使用的是vue-cli脚手架工具, 对于如何自己实现前端构建工具, 当下最为流行的就是webpack和gulp了, 之前一篇我们讲了gulp, 这一篇我们来好好讨论webpack.

说起webpack, 想必做前端的同学肯定不会陌生, 其实之前我们使用gulp构建的时候, 也使用了webpack的打包技术, 其实gulp和webpack并不是相互替代的关系, 而是相辅相成, 今天我们就来好好看看webpack的神奇之处吧.

我们学习一样新技术, 首先肯定是从他的官方文档入手, 当然我们要学习也是学最新版的.webpack的官方好代码教程写的非常好, 一步一步讲的很到位, 各位同学可以直接阅读官方文档, 比起博客中的二手, 三手以及四手的资料, 官方文档肯定是你更好的选择.

这篇文章, 不是教你什么看这一篇就够了之类的对于官方文档拷贝的水文, 而是能让你快速上手并且觉得所谓的webpack其实也就这么一回事, webpack你只要记住一个中心思想, 就和上面的图示一样, 将所有错综复杂的文件逻辑打包压缩成几个静态资源, 不多说了, 我们还是看代码来的实际.

webpack.config.js

对于一些抛弃jquery迎接react和vue的前端开发者来说, webpack虽然可能自己没有写过, 但看总是看过的吧, 一般来说, 都会有一个webpack.config.js的webpack配置文件.下面的代码就是一个简单的webpack的配置, 麻雀虽小五脏俱全.

var debug = process.env.NODE_ENV !== "production"; //是否是测试环境
var webpack = require('webpack'); //导入webpack包
var path = require('path');

module.exports = { //导出 webpack固定写法
 context: path.join(__dirname),
 devtool: debug ? "inline-sourcemap" : null, //是否使用map工具, 用于浏览器debug
 entry: "./src/js/root.js", //打包的实体
 module: {
  loaders: [ //加载的配置
   {
    test: /\.js?$/,
    exclude: /(node_modules)/,
    loader: 'babel-loader',
    query: {
     presets: ['react', 'es2015'], //添加预处理器
     plugins: ['react-html-attrs'], //添加组件的插件配置
    }
   },
   { test: /\.css$/, loader: 'style-loader!css-loader' },
   {
    test: /\.less$/,
    loader: "style!css!less"
   }
  ]
 },
 output: { //输出的路径及文件名
  path: __dirname,
  filename: "./src/bundle.js"
 },
 plugins: debug ? [] : [ //一些插件
  new webpack.optimize.DedupePlugin(),
  new webpack.optimize.OccurenceOrderPlugin(),
  new webpack.optimize.UglifyJsPlugin({ mangle: false, sourcemap: false }),
 ],
};

webpack主要包括entry, module, output, plugins四大类, 官方文档说的已经很清楚了, 想要进一步的学习,请翻阅官方文档, 如果不想折腾直接拷贝上述代码即可.

相较gulp, webpack在打包方面更为精简, 这也是流行的原因吧, 但光看上面的文件, 的确也是简单, 但是还有进一步改善的空间.

package.json

对于npm的介绍我就不多说了, 我们直接来看文件.

{
 "name": "webpack",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": { //命令行工具
  "test": "echo \"Error: no test specified\" && exit 1",
  "watch": "webpack --progress --watch",
  "start": "webpack-dev-server --open --config webpack.dev.js",
  "build": "webpack --config webpack.prod.js"
 },
 "keywords": [],
 "author": "",
 "license": "ISC",
 "devDependencies": { //开发环境依赖
  "babel-loader": "^7.1.2",
  "clean-webpack-plugin": "^0.1.16",
  "css-loader": "^0.28.7",
  "csv-loader": "^2.1.1",
  "file-loader": "^0.11.2",
  "html-webpack-plugin": "^2.30.1",
  "json-loader": "^0.5.7",
  "lodash": "^4.17.4",
  "style-loader": "^0.18.2",
  "uglifyjs-webpack-plugin": "^0.4.6",
  "webpack": "^3.6.0",
  "webpack-dev-middleware": "^1.12.0",
  "webpack-dev-server": "^2.8.2",
  "webpack-merge": "^4.1.0",
  "xml-loader": "^1.2.1"
 },
 "dependencies": { //生产环境依赖
  "babel-plugin-import": "^1.5.0",
  "babel-plugin-react-html-attrs": "^2.0.0",
  "babel-preset-es2015": "^6.24.1",
  "babel-preset-react": "^6.24.1",
  "babelify": "^7.3.0",
  "react": "^15.6.1",
  "react-dom": "^15.6.1",
  "react-mixin": "^4.0.0",
  "react-router": "^4.2.0"
 }
}

命令行工具就是npm run build等于执行了webpack --config webpack.prod.js, 而npm start 等于执行了webpack-dev-server --open --config webpack.dev.js.简单易懂吧.

在项目依赖中, 哦们加了很多的插件和loader, 都是用来搭建webpack的, 官方文档的好代码教程中都会讲到, 值得注意的就是webpack-merge这个包, 这个包可以让我们生产环境和开发环境很好的隔离配置, 我们看看怎么做呢?

首先我们需要将之前的webpack.config.js分成三个文件 --- webpack.common.js, webpack.dev.js, webpack.prod.js.

webpack.common.js

这个是webpack的共同配置, 总体和之前看到的大同小异, 我们主要是导入了两个插件, 一个是清除插件, 一个是创建html的插件.

const path = require('path');
const webpack = require('webpack');
const CleanWebpackPlugin = require('clean-webpack-plugin');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
 entry: './src/index.js',
 plugins: [
  new CleanWebpackPlugin(['dist']),
  new HtmlWebpackPlugin({title: 'webpack'}),
  new webpack.HashedModuleIdsPlugin()
 ],
 output: {
  filename: '[name].[chunkhash].js',
  path: path.resolve(__dirname, 'dist')
 },
 module: {
  rules: [
   {
    test: /\.js?$/,
    exclude: /(node_modules)/,
    loader: 'babel-loader',
    query: {
     presets: [
      'react', 'es2015'
     ],
     plugins: ['react-html-attrs']
    }
   },
   {
    test: /\.css$/,
    use: ['style-loader', 'css-loader']
   }, {
    test: /\.(png|svg|jpg|gif)$/,
    use: ['file-loader']
   }, {
    test: /\.(woff|woff2|eot|ttf|otf)$/,
    use: ['file-loader']
   }, {
    test: /\.(csv|tsv)$/,
    use: ['csv-loader']
   }, {
    test: /\.xml$/,
    use: ['xml-loader']
   }
  ]
 }
};

rules配置中我们也就是将一些可能用到的文件也配置到webpack中来, babel-loader这种如果要讲还可以再开一篇, 其实就是个js的兼容性工具, 这样理解就可以了.

webpack.dev.js

webpack开发环境的配置, 非常简单, 就是用了之前讲的webpack-merge工具, 就和git一样, 合并了webpack.common.js的配置外新加了可以进行调试的inline-source-map工具, 以及热更新的内容索引.

const merge = require('webpack-merge');
const common = require('./webpack.common.js');

module.exports = merge(common, {
 devtool: 'inline-source-map',
 devServer: {
  contentBase: './dist'
 }
});

webpack.prod.js

webpack生产环境的配置, 新加了一个压缩插件以及环境配置的插件, 这里的开发工具和开发还款下的有所不同, 具体可直接看官方文档.

const webpack = require('webpack');
const merge = require('webpack-merge');
const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
const common = require('./webpack.common.js');

module.exports = merge(common, {
 devtool: 'source-map',
 plugins: [
  new UglifyJSPlugin({sourceMap: true}),
  new webpack.DefinePlugin({
   'process.env': {
    'NODE_ENV': JSON.stringify('production')
   }
  })
 ]
});

terminal

这样我们就配置完成啦, 我们在终端上输入看下效果:

cd ../ && npm i 

首先我们进入到目录下并进行node包的安装.

npm run build

MacBook-Pro-15:webpack zhushuangquan$ npm run build

> webpack@1.0.0 build /Users/zhushuangquan/Documents/code/webpack
> webpack --config webpack.prod.js

clean-webpack-plugin: /Users/zhushuangquan/Documents/code/webpack/dist has been removed.
Hash: 85b65f54ef1436b295a5
Version: webpack 3.6.0
Time: 1148ms
              Asset    Size Chunks       Chunk Names
  main.014ac9aa420264da48eb.js 671 bytes    0 [emitted] main
main.014ac9aa420264da48eb.js.map  6.47 kB    0 [emitted] main
           index.html 197 bytes     [emitted] 
[lVK7] ./src/index.js 184 bytes {0} [built]
Child html-webpack-plugin for "index.html":
   1 asset
  [3IRH] (webpack)/buildin/module.js 517 bytes {0} [built]
  [DuR2] (webpack)/buildin/global.js 509 bytes {0} [built]
    + 2 hidden modules

我们可以看到已经打包好的文件:

main.014ac9aa420264da48eb.js

!function(e){function n(r){if(t[r])return t[r].exports;var o=t[r]={i:r,l:!1,exports:{}};return e[r].call(o.exports,o,o.exports,n),o.l=!0,o.exports}var t={};n.m=e,n.c=t,n.d=function(e,t,r){n.o(e,t)||Object.defineProperty(e,t,{configurable:!1,enumerable:!0,get:r})},n.n=function(e){var t=e&&e.__esModule?function(){return e.default}:function(){return e};return n.d(t,"a",t),t},n.o=function(e,n){return Object.prototype.hasOwnProperty.call(e,n)},n.p="",n(n.s="lVK7")}({lVK7:function(e,n,t){"use strict";document.body.appendChild(function(){var e=document.createElement("div");return e.innerHTML="Hello webpack",e}())}});
//# sourceMappingURL=main.014ac9aa420264da48eb.js.map

我们可以看到在webpack的打包和压缩下, 代码已经基本不可读了. 所以我们需要加上之前的调试插件, 以便生产环境出现bug后的补救.

npm start

MacBook-Pro-15:webpack zhushuangquan$ npm start

> webpack@1.0.0 start /Users/zhushuangquan/Documents/code/webpack
> webpack-dev-server --open --config webpack.dev.js

clean-webpack-plugin: /Users/zhushuangquan/Documents/code/webpack/dist has been removed.
Project is running at http://localhost:8080/
webpack output is served from /
Content not from webpack is served from ./dist
webpack: wait until bundle finished: /
Hash: 06f20ec519d58fbd5c28
Version: webpack 3.6.0
Time: 1460ms
            Asset    Size Chunks          Chunk Names
main.5eb4d4e3f458c49658a2.js   852 kB    0 [emitted] [big] main
         index.html 197 bytes     [emitted]     
[6Um2] (webpack)/node_modules/url/util.js 314 bytes {0} [built]
[8o/D] (webpack)-dev-server/client/overlay.js 3.71 kB {0} [built]
[HPf+] (webpack)/node_modules/url/url.js 23.3 kB {0} [built]
[Lx3u] (webpack)/hot/log.js 1.04 kB {0} [optional] [built]
[Sj28] (webpack)-dev-server/node_modules/strip-ansi/index.js 161 bytes {0} [built]
[TfA6] (webpack)/hot nonrecursive ^\.\/log$ 170 bytes {0} [built]
[U2me] (webpack)/hot/emitter.js 77 bytes {0} [built]
[V3KU] (webpack)-dev-server/client/socket.js 1.04 kB {0} [built]
[cMmS] (webpack)-dev-server/client?http://localhost:8080 7.27 kB {0} [built]
[gqsi] (webpack)-dev-server/node_modules/loglevel/lib/loglevel.js 7.74 kB {0} [built]
  [0] multi (webpack)-dev-server/client?http://localhost:8080 ./src/index.js 40 bytes {0} [built]
[gt+Q] (webpack)-dev-server/node_modules/ansi-regex/index.js 135 bytes {0} [built]
[lVK7] ./src/index.js 184 bytes {0} [built]
[p7Vd] (webpack)/node_modules/punycode/punycode.js 14.7 kB {0} [built]
[pEPF] (webpack)/node_modules/querystring-es3/index.js 127 bytes {0} [built]
  + 73 hidden modules
Child html-webpack-plugin for "index.html":
   1 asset
  [3IRH] (webpack)/buildin/module.js 517 bytes {0} [built]
  [DuR2] (webpack)/buildin/global.js 509 bytes {0} [built]
  [M4fF] ./node_modules/lodash/lodash.js 540 kB {0} [built]
  [a/t9] ./node_modules/html-webpack-plugin/lib/loader.js!./node_modules/html-webpack-plugin/default_index.ejs 538 bytes {0} [built]
webpack: Compiled successfully.

我们可以看到打开了一个内容为Hello webpack的网页在8080端口, 当我们修改了文件时候网页会自动刷新.

知识点:

回到我们刚才的package.json的命令行配置来看.

 "scripts": { //命令行工具
  "test": "echo \"Error: no test specified\" && exit 1",
  "watch": "webpack --progress --watch",
  "start": "webpack-dev-server --open --config webpack.dev.js",
  "build": "webpack --config webpack.prod.js"
 },

• 上面的npm run build => webpack => webpack.prod.js, 就是执行了生产环境的配置的打包命令.
• 上面的npm start => webpack-dev-server --open => webpack.dev.js, 就是执行了开发环境配置的服务端命令.
• --config是用于执行webpack配置文件的命令, 而默认为webpack.config.js.
• webpack命令就是和之前的gulp的逻辑相似, 将entry实例复制到output路径的逻辑. 当然还伴随着一系列的操作.
• webpack-dev-server --open命令是打开服务器并进行热加载的用途.

以上就是webpack的使用及逻辑, 并没有想象中的复杂吧, 甚至可以说是简单, 实测一天即可入门webpack.

由于webpack的配置是固定代码, 我已经打包上传github, 需要的同学可以进行下载.