14. vue源码入口+项目结构分析

一. vue源码

我们安装好vue以后， 如何了解vue的的代码结构， 从哪里下手呢？

1.1. vue源码入口

vue的入口是package.json

来分别看看是什么含义

• dependences：

  "dependencies": {
    "vue": "^2.5.2"
  },

这段代码告诉我们vue的版本： 2.5.2

• engines

  "engines": {
    "node": ">= 6.0.0",
    "npm": ">= 3.0.0"
  },

指定当前node的版本和npm的版本

• devDependencies
  
  里面是引入的各种loader

• scripts

  "scripts": {
    "dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
    "start": "npm run dev",
    "build": "node build/build.js"
  },

这就是重点了。 我们npm run build、npm run dev都是执行这里面的命令。 他告诉我们当执行build的时候是在执行那个文件。

1. dev： 读取的配置文件是build/webpack.dev.conf.js
2. build: 读取的配置文件是buld/build.js

1.2.项目文件的结构

先来看看项目的整体目录结构

1.2.1. webpack相关配置

1.2.1.1 webpack.dev.config.js是本地开发环境读取配置文件。

'use strict'
// 定义变量, 生产环境和开发环境区别定义
const utils = require('./utils')
const webpack = require('webpack')
const config = require('../config')
const merge = require('webpack-merge')
const path = require('path')
// 引入公共配置
const baseWebpackConfig = require('./webpack.base.conf')
/**
 * 引入插件
 */
// 版权插件
const CopyWebpackPlugin = require('copy-webpack-plugin')
// 打包html到dist文件下, 并自动引入main.js文件
const HtmlWebpackPlugin = require('html-webpack-plugin')
//友好的错误提示插件
const FriendlyErrorsPlugin = require('friendly-errors-webpack-plugin')
const portfinder = require('portfinder')

const HOST = process.env.HOST
const PORT = process.env.PORT && Number(process.env.PORT)

// merge函数: 将两个配置和并. 这里是将基础配置和开发环境的配置进行合并
const devWebpackConfig = merge(baseWebpackConfig, {
  module: {
    rules: utils.styleLoaders({ sourceMap: config.dev.cssSourceMap, usePostCSS: true })
  },
  // cheap-module-eval-source-map is faster for development
  devtool: config.dev.devtool,

  // these devServer options should be customized in /config/index.js
  devServer: {
    clientLogLevel: 'warning',
    historyApiFallback: {
      rewrites: [
        { from: /.*/, to: path.posix.join(config.dev.assetsPublicPath, 'index.html') },
      ],
    },
    hot: true,
    contentBase: false, // since we use CopyWebpackPlugin.
    compress: true,
    host: HOST || config.dev.host,
    port: PORT || config.dev.port,
    open: config.dev.autoOpenBrowser,
    overlay: config.dev.errorOverlay
      ? { warnings: false, errors: true }
      : false,
    publicPath: config.dev.assetsPublicPath,
    proxy: config.dev.proxyTable,
    quiet: true, // necessary for FriendlyErrorsPlugin
    watchOptions: {
      poll: config.dev.poll,
    }
  },
  // 开发环境引入的插件
  plugins: [
    new webpack.DefinePlugin({
      'process.env': require('../config/dev.env')
    }),
    new webpack.HotModuleReplacementPlugin(),
    new webpack.NamedModulesPlugin(), // HMR shows correct file names in console on update.
    new webpack.NoEmitOnErrorsPlugin(),
    // https://github.com/ampedandwired/html-webpack-plugin
    new HtmlWebpackPlugin({
      filename: 'index.html',
      template: 'index.html',
      inject: true
    }),
    // copy custom static assets
    new CopyWebpackPlugin([
      {
        from: path.resolve(__dirname, '../static'),
        to: config.dev.assetsSubDirectory,
        ignore: ['.*']
      }
    ])
  ]
})

module.exports = new Promise((resolve, reject) => {
  portfinder.basePort = process.env.PORT || config.dev.port
  portfinder.getPort((err, port) => {
    if (err) {
      reject(err)
    } else {
      // publish the new Port, necessary for e2e tests
      process.env.PORT = port
      // add port to devServer config
      devWebpackConfig.devServer.port = port

      // Add FriendlyErrorsPlugin
      devWebpackConfig.plugins.push(new FriendlyErrorsPlugin({
        compilationSuccessInfo: {
          messages: [`Your application is running here: http://${devWebpackConfig.devServer.host}:${port}`],
        },
        onErrors: config.dev.notifyOnErrors
        ? utils.createNotifierCallback()
        : undefined
      }))

      resolve(devWebpackConfig)
    }
  })
})

• webpack.base.conf: 引入了基础项目配置。 公共的配置文件（开发和生产都会使用到的配置文件）都写到这里
• 引入插件： 版权插件、html文件打包插件、有好错题提示插件
• 引入merge包， 将基础配置文件和当前文件合并。

1.2.1.2 build.js是build打包时读取的配置文件

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

process.env.NODE_ENV = 'production'

const ora = require('ora')
const rm = require('rimraf')
const path = require('path')
const chalk = require('chalk')
const webpack = require('webpack')
const config = require('../config')
// 引入了prod配置文件
const webpackConfig = require('./webpack.prod.conf')

...

我们看到build.js引入了webpack.prod.conf配置文件

下面就来看看webpack.prod.conf配置文件都有哪些内容

'use strict'
// 生产环境个性化配置
const path = require('path')
const utils = require('./utils')
// 引入webpack打包工具
const webpack = require('webpack')
const config = require('../config')
// 引入配置合并工具
const merge = require('webpack-merge')
// 引入基础配置文件
const baseWebpackConfig = require('./webpack.base.conf')
// 引入版权配置插件
const CopyWebpackPlugin = require('copy-webpack-plugin')
// 引入html配置合并
const HtmlWebpackPlugin = require('html-webpack-plugin')
// 引入text打包工具
const ExtractTextPlugin = require('extract-text-webpack-plugin')
// 引入css打包工具
const OptimizeCSSPlugin = require('optimize-css-assets-webpack-plugin')
// 引入js压缩工具
const UglifyJsPlugin = require('uglifyjs-webpack-plugin')

// 引入生产环境的配置文件
const env = require('../config/prod.env')

// merge: 将基础配置 + 生产的个性化配置合并
const webpackConfig = merge(baseWebpackConfig, {
  module: {
    rules: utils.styleLoaders({
      sourceMap: config.build.productionSourceMap,
      extract: true,
      usePostCSS: true
    })
  },
  devtool: config.build.productionSourceMap ? config.build.devtool : false,
  output: {
    path: config.build.assetsRoot,
    filename: utils.assetsPath('js/[name].[chunkhash].js'),
    chunkFilename: utils.assetsPath('js/[id].[chunkhash].js')
  },
  // 生成环境需要使用的插件
  plugins: [
    // http://vuejs.github.io/vue-loader/en/workflow/production.html
    new webpack.DefinePlugin({
      'process.env': env
    }),
    new UglifyJsPlugin({
      uglifyOptions: {
        compress: {
          warnings: false
        }
      },
      sourceMap: config.build.productionSourceMap,
      parallel: true
    }),
    // extract css into its own file
    new ExtractTextPlugin({
      filename: utils.assetsPath('css/[name].[contenthash].css'),
      // Setting the following option to `false` will not extract CSS from codesplit chunks.
      // Their CSS will instead be inserted dynamically with style-loader when the codesplit chunk has been loaded by webpack.
      // It's currently set to `true` because we are seeing that sourcemaps are included in the codesplit bundle as well when it's `false`,
      // increasing file size: https://github.com/vuejs-templates/webpack/issues/1110
      allChunks: true,
    }),
    // Compress extracted CSS. We are using this plugin so that possible
    // duplicated CSS from different components can be deduped.
    new OptimizeCSSPlugin({
      cssProcessorOptions: config.build.productionSourceMap
        ? { safe: true, map: { inline: false } }
        : { safe: true }
    }),
    // generate dist index.html with correct asset hash for caching.
    // you can customize output by editing /index.html
    // see https://github.com/ampedandwired/html-webpack-plugin
    // html打包插件: 比如:将index.html打包到dist文件夹中.并自动引入bundle.js文件
    new HtmlWebpackPlugin({
      filename: config.build.index,
      template: 'index.html',
      inject: true,
      minify: {
        removeComments: true,
        collapseWhitespace: true,
        removeAttributeQuotes: true
        // more options:
        // https://github.com/kangax/html-minifier#options-quick-reference
      },
      // necessary to consistently work with multiple chunks via CommonsChunkPlugin
      chunksSortMode: 'dependency'
    }),
    // keep module.id stable when vendor modules does not change
    new webpack.HashedModuleIdsPlugin(),
    // enable scope hoisting
    new webpack.optimize.ModuleConcatenationPlugin(),
    // split vendor js into its own file
    new webpack.optimize.CommonsChunkPlugin({
      name: 'vendor',
      minChunks (module) {
        // 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',
      minChunks: Infinity
    }),
    // This instance extracts shared chunks from code splitted chunks and bundles them
    // in a separate chunk, similar to the vendor chunk
    // see: https://webpack.js.org/plugins/commons-chunk-plugin/#extra-async-commons-chunk
    new webpack.optimize.CommonsChunkPlugin({
      name: 'app',
      async: 'vendor-async',
      children: true,
      minChunks: 3
    }),

    // copy custom static assets
    new CopyWebpackPlugin([
      {
        from: path.resolve(__dirname, '../static'),
        to: config.build.assetsSubDirectory,
        ignore: ['.*']
      }
    ])
  ]
})

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

module.exports = webpackConfig

• 这prod.config.js中引入了webpack.base.conf
• 引入了一些插件： 版权配置插件， html打包插件，text打包工具、css打包压缩工具、js压缩工具。
• 读取了config/prod.env配置文件。
• 使用merge合并基础配置

1.2.2 .babelrc配置文件：ES代码相关转化配置

{
  "presets": [
    ["env", {
      "modules": false,
      "targets": {
        "browsers": ["> 1%", "last 2 versions", "not ie <= 8"]
      }
    }],
    "stage-2"
  ],
  "plugins": ["transform-vue-jsx", "transform-runtime"]
}

这是将es6的语法转换成es5. 转换的目标是什么呢

"browsers": ["> 1%", "last 2 versions", "not ie <= 8"]

1. 市场份额大于1%
2. 转换浏览器的最后两个版本
3. ie8以下的版本不转化

1.2.3 .editorconfig文本编辑相关配置

root = true

[*]
charset = utf-8
indent_style = space
indent_size = 2
end_of_line = lf
insert_final_newline = true
trim_trailing_whitespace = true

• charset: 配置文本的字符编码格式
• indent_style: 默认的缩进方式是空格
• indent_size: 缩进空格数是2个
• end_of_line: 尾部处理方式
• insert_final_newline: 尾部自动增加一个单行
• trim_trailing_whitespace: 是否自动格式化空格

1.2.4 .eslintrc.js esLint相关的设置

esLint格式化内容配置, 我们可以启动或者关闭eslint.

1.3. vue访问入口

vue的访问入口是index.html, 当我们执行

npm run dev

的时候， 其实是将文件打包的过程， 和npm run build的区别是， 它是将文件打包到内存。 然后运行在本地服务器。而npm run build是打包到磁盘dist文件夹

1.3.1 访问入口

vue访问的入口是main.js

// The Vue build version to load with the `import` command
// (runtime-only or standalone) has been set in webpack.base.conf with an alias.
import Vue from 'vue'
import App from './App'
import router from './router'

Vue.config.productionTip = false

/* eslint-disable no-new */
new Vue({
  el: '#app',
  router,
  components: { App },
  template: '<App/>'
})

• 引入了vue
• 引入了./App.vue， 当前目录的App.vue配置文件
• 当前vue的作用dom元素是id="app"的元素
• 引入了App组件。 App组件，定义在App.vue中
• 使用App组件替代id="app"的元素。

下面来看看App.vue

<template>
  <div id="app">
    <img src="./assets/logo.png">
    <HelloWorld/>
  </div>
</template>

<script>
import HelloWorld from './components/HelloWorld'

export default {
  name: 'App',
  components: {
    HelloWorld
  }
}
</script>

<style>
#app {
  font-family: 'Avenir', Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

• 首先引入了HelloWorld组件

import HelloWorld from './components/HelloWorld'

• 将组件注册到名为App的组件中
• 在模板中引入HelloWorld组件

然后，我们就看到vue首页的效果了。了解源码入口，方便我们后续代码.