執(zhí)行npm run dev或者npm run start，實際是在node環(huán)境執(zhí)行build/dev-server.js, dev-server.js會去拿到config中的端口等配置算利，通過express起一個服務(wù)册踩，通過插件自動打開瀏覽器，加載webpack編譯后放在內(nèi)存的bundle效拭。

//執(zhí)行npm run build暂吉，實際上執(zhí)行了build/build.js,通過webpack的一系列配置及插件，將文件打包合并丑化缎患，并創(chuàng)建dist目錄借笙，放置編譯打包后的文件，這將是未來用在生產(chǎn)環(huán)境的包较锡。

//現(xiàn)代的前端項目中通常都會有package.json文件。在package.json里盗痒，會介紹項目名稱蚂蕴、版本、描述俯邓、作者骡楼、腳本、依賴包稽鞭，對環(huán)境的要求鸟整，以及對瀏覽器要求。
{
  "name": "uccn",
  "version": "1.0.0",
  "description": "uccn3.0",
  "author": "v_yangtianjiao <v_yangtianjiao@baidu.com>",
  "private": true,
　　　// 這里的腳本是分析項目的主要入口
  "scripts": {
    "dev": "node build/dev-server.js",
    "start": "node build/dev-server.js",
    "build": "node build/build.js",
    "jsonp": "node build/jsonp-server.js"
  },
　　　// 項目依賴
  "dependencies": {
    "fetch-jsonp": "^1.1.3",
    "less": "^2.7.2",
    "less-loader": "^4.0.4",
    "stylus": "^0.54.5",
    "stylus-loader": "^3.0.1",
    "vue": "^2.4.2"
  },
  "devDependencies": {
    "autoprefixer": "^7.1.2",
    "babel-core": "^6.22.1",
    "babel-loader": "^7.1.1",
    "babel-plugin-component": "^0.10.1",
    "babel-plugin-transform-runtime": "^6.22.0",
    "babel-preset-env": "^1.3.2",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-stage-2": "^6.22.0",
    "babel-register": "^6.22.0",
    "chalk": "^2.0.1",
    "connect-history-api-fallback": "^1.3.0",
    "copy-webpack-plugin": "^4.0.1",
    "css-loader": "^0.28.0",
    "cssnano": "^3.10.0",
    "eventsource-polyfill": "^0.9.6",
    "express": "^4.14.1",
    "extract-text-webpack-plugin": "^2.0.0",
    "file-loader": "^0.11.1",
    "friendly-errors-webpack-plugin": "^1.1.3",
    "html-webpack-plugin": "^2.28.0",
    "http-proxy-middleware": "^0.17.3",
    "opn": "^5.1.0",
    "optimize-css-assets-webpack-plugin": "^2.0.0",
    "ora": "^1.2.0",
    "rimraf": "^2.6.0",
    "semver": "^5.3.0",
    "shelljs": "^0.7.6",
    "url-loader": "^0.5.8",
    "vue-loader": "^13.0.4",
    "vue-style-loader": "^3.0.1",
    "vue-template-compiler": "^2.4.2",
    "webpack": "^2.6.1",
    "webpack-bundle-analyzer": "^2.2.1",
    "webpack-dev-middleware": "^1.10.0",
    "webpack-hot-middleware": "^2.18.0",
    "webpack-merge": "^4.1.0"
  },
     // 對node版本的以及npm版本的要求
  "engines": {
    "node": ">= 4.0.0",
    "npm": ">= 3.0.0"
  },
　　　// 瀏覽器要求朦蕴，vue項目不支持ie8篮条，因為ie8是es3，尚沒有Object.defineProperty屬性
  "browserslist": [
    "> 1%",
    "last 2 versions",
    "not ie <= 8"
  ]
}

/* eslint-disable */

// 首先檢查node和npm的版本
require('./check-versions')()

// 獲取配置文件中默認(rèn)的配置
var config = require('../config')
// 如果node無法判斷當(dāng)前是開發(fā)環(huán)境還是生產(chǎn)環(huán)境吩抓，則使用config.dev.env.NODE_ENV作為當(dāng)前的環(huán)境
if (!process.env.NODE_ENV) {
  process.env.NODE_ENV = JSON.parse(config.dev.env.NODE_ENV)
}

var opn = require('opn')// 用來在起來服務(wù)之后涉茧，打開瀏覽器并跳轉(zhuǎn)指定URL
var path = require('path')// node自帶文件路徑工具
var express = require('express')// node框架express（本地開發(fā)的核心，起服務(wù)）
var webpack = require('webpack')// webpack,壓縮打包
var proxyMiddleware = require('http-proxy-middleware')// 中間件
var webpackConfig = require('./webpack.dev.conf')// 開發(fā)環(huán)境的webpack配置
var mockMiddleware = require('../config/dev.mock')// 開發(fā)環(huán)境本地mock數(shù)據(jù)中間件

var port = process.env.PORT || config.dev.port
var autoOpenBrowser = !!config.dev.autoOpenBrowser
var proxyTable = config.dev.proxyTable

var app = express()// 起服務(wù)
var compiler = webpack(webpackConfig)// webpack進行編譯

// webpack-dev-middleware將編譯的文件放在內(nèi)存中疹娶，后續(xù)注入
var devMiddleware = require('webpack-dev-middleware')(compiler, {
  publicPath: webpackConfig.output.publicPath,
  quiet: true
})
// 熱加載
var hotMiddleware = require('webpack-hot-middleware')(compiler, {
  log: false,
  heartbeat: 2000
})
compiler.plugin('compilation', function (compilation) {
  compilation.plugin('html-webpack-plugin-after-emit', function (data, cb) {
    hotMiddleware.publish({ action: 'reload' })
    cb()
  })
})

// proxy api requests
// proxyTable中的配置掛載到express中
Object.keys(proxyTable).forEach(function (context) {
  var options = proxyTable[context]
  if (typeof options === 'string') {
    options = { target: options }
  }
  app.use(proxyMiddleware(options.filter || context, options))
})

// 處理后退的時候匹配資源
app.use(require('connect-history-api-fallback')())

// 暫存在內(nèi)存的webpack編譯后的文件掛載到express上
app.use(devMiddleware)

// 將本地mock中間件掛載到express上
app.use(mockMiddleware);

// 熱加載掛載到express上
app.use(hotMiddleware)

// 拼static靜態(tài)資源文件路徑
var staticPath = path.posix.join(config.dev.assetsPublicPath, config.dev.assetsSubDirectory)
// express為靜態(tài)資源提供服務(wù)
app.use(staticPath, express.static('./static'))

var uri = 'http://localhost:' + port

var _resolve
var readyPromise = new Promise(resolve => {
  _resolve = resolve
})

console.log('> Starting dev server...')
devMiddleware.waitUntilValid(() => {
  console.log('> Listening at ' + uri + '\n')
  if (autoOpenBrowser && process.env.NODE_ENV !== 'testing') {
    opn(uri)
  }
  _resolve()
})
// 通過配置的端口伴栓，自動打開瀏覽器，并跳轉(zhuǎn)拼好的URL雨饺，至此钳垮，發(fā)開環(huán)境已經(jīng)跑起來了
var server = app.listen(port)

module.exports = {
  ready: readyPromise,
  close: () => {
    server.close()
  }
}

// node自帶路徑工具.
var path = require('path')
// 分為兩種環(huán)境，dev和production
module.exports = {
  build: {
    env: require('./prod.env'),// 使用config/prod.env.js中定義的編譯環(huán)境
    index: path.resolve(__dirname, '../dist/index.html'),// 編譯輸入的index.html文件额港。node.js中饺窿，在任何模塊文件內(nèi)部，可以使用__filename變量獲取當(dāng)前模塊文件的帶有完整絕對路徑的文件名,
    assetsRoot: path.resolve(__dirname, '../dist'),// 編譯輸出的靜態(tài)資源路徑
    assetsSubDirectory: 'static',// 編譯輸出的二級目錄
    assetsPublicPath: './', // 編譯發(fā)布的根目錄移斩，可配置為資源服務(wù)器或者cdn域名
    productionSourceMap: false,//是否開啟cssSourceMap
    productionGzip: false,// 是否開啟gzip
    productionGzipExtensions: ['js', 'css'],// 需要用gzip壓縮的文件擴展名
    bundleAnalyzerReport: process.env.npm_config_report
  },
  dev: {
    env: require('./dev.env'),
    port: 8989,// 起服務(wù)的端口
    autoOpenBrowser: true,
    assetsSubDirectory: 'static',
    assetsPublicPath: '/',
    proxyTable: {},// 需要代理的接口短荐，可以跨域
    cssSourceMap: false
  }
}

var utils = require('./utils')// 工具類
var webpack = require('webpack')
var config = require('../config')
var merge = require('webpack-merge')// 使用webpack配置合并插件
var baseWebpackConfig = require('./webpack.base.conf')
var HtmlWebpackPlugin = require('html-webpack-plugin')// 這個插件自動生成HTML倚舀，并注入到.html文件中
var FriendlyErrorsPlugin = require('friendly-errors-webpack-plugin')

// 將hot-reload相對路徑添加到webpack.base.conf的對應(yīng)的entry前面
Object.keys(baseWebpackConfig.entry).forEach(function (name) {
  baseWebpackConfig.entry[name] = ['./build/dev-client'].concat(baseWebpackConfig.entry[name])
})

// webpack.dev.conf.js與webpack.base.conf.js中的配置合并
module.exports = merge(baseWebpackConfig, {
  module: {
    rules: utils.styleLoaders({ sourceMap: config.dev.cssSourceMap })
  },
  // webpack-devtool有7種模式，cheap-module-eval-source-map模式是比較快的開發(fā)模式
　
  devtool: '#cheap-module-eval-source-map',
  plugins: [
　　// 你可以理解為忍宋，通過配置了DefinePlugin痕貌，那么這里面的標(biāo)識就相當(dāng)于全局變量，你的業(yè)務(wù)代碼可以直接使用配置的標(biāo)識糠排。
    new webpack.DefinePlugin({
      'process.env': config.dev.env
    }),
    // hotModule插件讓頁面變動時舵稠，只重繪對應(yīng)的模塊，不會重繪整個HTML文件
    new webpack.HotModuleReplacementPlugin(),
　　// 在編譯出現(xiàn)錯誤時入宦，使用 NoEmitOnErrorsPlugin 來跳過輸出階段哺徊。這樣可以確保輸出資源不會包含錯誤
    new webpack.NoEmitOnErrorsPlugin(),
    // 將生成的HTML代碼注入index.html文件
    new HtmlWebpackPlugin({
      filename: 'index.html',
      template: 'index.html',
      inject: true
    }),
　　// friendly-errors-webpack-plugin用于更友好地輸出webpack的警告、錯誤等信息
    new FriendlyErrorsPlugin()
  ]
})

/* eslint-disable */
var path = require('path')// node自帶的文件路徑插件
var utils = require('./utils')// 工具類
var config = require('../config')// 上面說過的config/index
var vueLoaderConfig = require('./vue-loader.conf')// vue-loader.conf配置文件是用來解決各種css文件的乾闰，定義了諸如css,less,sass之類的和樣式有關(guān)的loader
// 此函數(shù)是用來返回當(dāng)前目錄的平行目錄的路徑落追，
function resolve (dir) {
  return path.join(__dirname, '..', dir)
}

module.exports = {
  entry: {
    uccn: './src/main.js'// 入口
  },
  output: {
　　// 路徑是config目錄下的index.js中的build配置中的assetsRoot，也就是dist目錄
    path: config.build.assetsRoot,
    filename: '[name].js',
　　// 上線地址涯肩，也就是真正的文件引用路徑轿钠，如果是production生產(chǎn)環(huán)境，其實這里都是 '/'
    publicPath: process.env.NODE_ENV === 'production'
      ? config.build.assetsPublicPath
      : config.dev.assetsPublicPath
  },
　// resolve是webpack的內(nèi)置選項病苗，顧名思義疗垛，決定要做的事情，也就是說當(dāng)使用 import "jquery"硫朦，該如何去執(zhí)行這件事情贷腕，就是resolve配置項要做的，import jQuery from "./additional/dist/js/jquery" 這樣會很麻煩咬展，可以起個別名簡化操作
  resolve: {
　　// 省略擴展名泽裳，比方說import index form '../js/index', 會默認(rèn)去找index文件，然后找index.js,.vue,.josn.
    extensions: ['.js', '.vue', '.json'],
    alias: {
      'vue$': 'vue/dist/vue.esm.js',
　　　　// 使用上面的resolve函數(shù)破婆，意思是用@代替src的絕對路徑
      '@': resolve('src'),
    }
  },
　// 不同的模塊使用不同的loader
  module: {
    rules: [
      {
　　　　　// 對vue文件诡壁，使用vue-loader解析
        test: /\.vue$/,
        loader: 'vue-loader',
        options: vueLoaderConfig
      },
      {
　　　　　// babel-loader把es6解析成es5
        test: /\.js$/,
        loader: 'babel-loader',
        include: [resolve('src'), resolve('test')]
      },
      {
　　　　　// url-loader將文件大小低于下面option中l(wèi)imit的圖片，轉(zhuǎn)化為一個64位的DataURL荠割，這樣會省去很多請求妹卿，大于limit的，按[name].[hash:7].[ext]的命名方式放到了static/img下面蔑鹦，方便做cache
        test: /\.(png|jpe?g|gif|svg)(\?.*)?$/,
        loader: 'url-loader',
        options: {
          limit: 20000,
          name: utils.assetsPath('img/[name].[hash:7].[ext]')
        }
      },
      {
　　　　　// 音頻和視頻文件處理夺克，同上
        test: /\.(mp4|webm|ogg|mp3|wav|flac|aac)(\?.*)?$/,
        loader: 'url-loader',
        options: {
          limit: 10000,
          name: utils.assetsPath('media/[name].[hash:7].[ext]')
        }
      },
      {
　　　　　// 字體處理，同上　
        test: /\.(woff2?|eot|ttf|otf)(\?.*)?$/,
        loader: 'url-loader',
        options: {
          limit: 10000,
          name: utils.assetsPath('fonts/[name].[hash:7].[ext]')
        }
      }
    ]
  }
}

var path = require('path')
var config = require('../config')
// extract-text-webpack-plugin該插件的主要是為了抽離css樣式,防止將樣式打包在js中引起頁面樣式加載錯亂的現(xiàn)象
var ExtractTextPlugin = require('extract-text-webpack-plugin')

// 返回資源文件路徑嚎朽，path.posix以posix兼容的方式交互铺纽，是跨平臺的，如果是path.win32的話哟忍，只能在win上
exports.assetsPath = function (_path) {
  var assetsSubDirectory = process.env.NODE_ENV === 'production'
    ? config.build.assetsSubDirectory
    : config.dev.assetsSubDirectory
  return path.posix.join(assetsSubDirectory, _path)
}

// 通過判斷是否是生產(chǎn)環(huán)境狡门，配置不同的樣式語言的loader配置
exports.cssLoaders = function (options) {
  options = options || {}

  var cssLoader = {
    loader: 'css-loader',
    options: {
      minimize: process.env.NODE_ENV === 'production',
      sourceMap: options.sourceMap
    }
  }

  // 生成各種loader配置陷寝，通過傳入不同的loader和option，將不同樣式文件語言的loader拼好其馏，push到loader配置中凤跑。
  function generateLoaders (loader, loaderOptions) {
    var loaders = [cssLoader]
    if (loader) {
      loaders.push({
        loader: loader + '-loader',
        options: Object.assign({}, loaderOptions, {
          sourceMap: options.sourceMap
        })
      })
    }

    // extract-text-webpack-plugin有三個參數(shù)，use指需要用什么loader去編譯文件叛复；fallback指編譯后用什么loader去提取文件仔引；還有一個publicfile用來覆蓋項目路徑
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // 對不同的樣式語言，返回相應(yīng)的loader
  return {
    css: generateLoaders(),
    postcss: generateLoaders(),
    less: generateLoaders('less'),
    sass: generateLoaders('sass', { indentedSyntax: true }),
    scss: generateLoaders('sass'),
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }
}

// 生成處理不同的樣式文件處理規(guī)則
exports.styleLoaders = function (options) {
  var output = []
  var loaders = exports.cssLoaders(options)
  for (var extension in loaders) {
    var loader = loaders[extension]
    output.push({
      test: new RegExp('\\.' + extension + '$'),
      use: loader
    })
  }
  return output
}

require('./check-versions')()

process.env.NODE_ENV = 'production'

// 在終端顯示的旋轉(zhuǎn)器插件
var ora = require('ora')
// 用于刪除文件夾
var rm = require('rimraf')
var path = require('path')
// 終端文字顏色插件
var chalk = require('chalk')
var webpack = require('webpack')
var config = require('../config')
var webpackConfig = require('./webpack.prod.conf')

var spinner = ora('building for production...')
spinner.start()

// 刪除dist文件夾褐奥，之后webpack打包
rm(path.join(config.build.assetsRoot, config.build.assetsSubDirectory), err => {
  if (err) throw err
  webpack(webpackConfig, function (err, stats) {
    spinner.stop()
    if (err) throw err
    process.stdout.write(stats.toString({
      colors: true,
      modules: false,
      children: false,
      chunks: false,
      chunkModules: false
    }) + '\n\n')

    if (stats.hasErrors()) {
      console.log(chalk.red('  Build failed with errors.\n'))
      process.exit(1)
    }

    console.log(chalk.cyan('  Build complete.\n'))
    console.log(chalk.yellow(
      '  Tip: built files are meant to be served over an HTTP server.\n' +
      '  Opening index.html over file:// won\'t work.\n'
    ))
  })
})

/* eslint-disable */
var path = require('path')
var utils = require('./utils')
var webpack = require('webpack')
var config = require('../config')
var merge = require('webpack-merge')
var baseWebpackConfig = require('./webpack.base.conf')
var CopyWebpackPlugin = require('copy-webpack-plugin')
var HtmlWebpackPlugin = require('html-webpack-plugin')
// 用于從webpack生成的bundle中提取文本到特定文件中的插件
// 可以抽取出css咖耘，js文件將其與webpack輸出的bundle分離
var ExtractTextPlugin = require('extract-text-webpack-plugin')
var OptimizeCSSPlugin = require('optimize-css-assets-webpack-plugin')

var env = config.build.env
// 合并基礎(chǔ)的webpack配置
var webpackConfig = merge(baseWebpackConfig, {
  module: {
    rules: utils.styleLoaders({
      sourceMap: config.build.productionSourceMap,
      extract: true
    })
  },
　// 7中sourceMap上面有講過
  devtool: config.build.productionSourceMap ? '#source-map' : false,
　// 配置webpack輸出的目錄，及文件命名規(guī)則
  output: {
    path: config.build.assetsRoot,
    filename: utils.assetsPath('js/[name].min.js'),
    chunkFilename: utils.assetsPath('js/[id].[chunkhash].js')
  },
　// webpack插件配置
  plugins: [
    // 同webpack.dev.conf.js
    new webpack.DefinePlugin({
      'process.env': env
    }),
　　// 丑化代碼
    new webpack.optimize.UglifyJsPlugin({
      compress: {
        warnings: false
      },
      sourceMap: true
    }),
    // 抽離css文件到單獨的文件
    new ExtractTextPlugin({
      filename: utils.assetsPath('css/[name].min.css')
    }),
    new OptimizeCSSPlugin({
      cssProcessorOptions: {
        safe: true
      }
    }),
    // 生成并注入index.html
    new HtmlWebpackPlugin({
      filename: config.build.index,
      template: 'index.html',
      inject: true,
      minify: {
        removeComments: true,
        collapseWhitespace: false,
        removeAttributeQuotes: true
      },
      chunksSortMode: 'dependency'
    }),
    // keep module.id stable when vender modules does not change
    new webpack.HashedModuleIdsPlugin(),
    split vendor js into its own file
    new webpack.optimize.CommonsChunkPlugin({
      name: 'vendor',
      minChunks: function (module, count) {
        // any required modules inside node_modules are extracted to vendor
        return (
          module.resource &&
          /\.js$/.test(module.resource) &&
          module.resource.indexOf(
            path.join(__dirname, '../node_modules')
          ) === 0
        )
      }
    }),
    extract webpack runtime and module manifest to its own file in order to
    prevent vendor hash from being updated whenever app bundle is updated
    new webpack.optimize.CommonsChunkPlugin({
      name: 'manifest',
      chunks: ['vendor']
    }),
    copy custom static assets
    new CopyWebpackPlugin([
      {
        from: path.resolve(__dirname, '../static'),
        to: config.build.assetsSubDirectory,
        ignore: ['.*']
      }
    ])
  ]
})
// gzip模式下需要引入compression插件進行壓縮
if (config.build.productionGzip) {
  var CompressionWebpackPlugin = require('compression-webpack-plugin')

  webpackConfig.plugins.push(
    new CompressionWebpackPlugin({
      asset: '[path].gz[query]',
      algorithm: 'gzip',
      test: new RegExp(
        '\\.(' +
        config.build.productionGzipExtensions.join('|') +
        ')$'
      ),
      threshold: 10240,
      minRatio: 0.8
    })
  )
}

if (config.build.bundleAnalyzerReport) {
  var BundleAnalyzerPlugin = require('webpack-bundle-analyzer').BundleAnalyzerPlugin
  webpackConfig.plugins.push(new BundleAnalyzerPlugin())
}

module.exports = webpackConfig