webpack编译流程

1. webpack编译流程

• 初始化参数：从配置文件和Shell语句中读取与合并参数，得出最终的参数；
• 开始编译：用上一步得到的参数初始化Compiler对象，加载所有配置的插件，执行对象的run方法开始执行编译； 确定入口：根据配置中的entry找出所有的入口文件
• 编译模块：从入口文件出发，调用所有配置的Loader对模块进行编译，再找出该模块依赖的模块，再递归本步骤直到所有入口依赖的文件都经过了本步骤的处理；
• 完成模块编译：在经过第4步使用Loader翻译完所有模块后，得到了每个模块被翻译后的最终内容以及它们之间的依赖关系
• 输出资源：根据入口和模块之间的依赖关系，组装成一个个包含多个模块的 Chunk，再把每个Chunk转换成一个单独的文件加入到输出列表，这步是可以修改输出内容的最后机会
• 输出完成：在确定好输出内容后，根据配置确定输出的路径和文件名，把文件内容写入到文件系统

在以上过程中，Webpack 会在特定的时间点广播出特定的事件，插件在监听到感兴趣的事件后会执行特定的逻辑，并且插件可以调用 Webpack 提供的 API 改变 Webpack 的运行结果

webpackflowes

2.调试webpack

• cli

2.1 如何生成调试文件

• 打开工程目录，点击调试按钮，再点击小齿轮的配置按钮系统就会生成launch.json配置文件
• 修改好了以后直接点击F5就可以启动调试

.vscode\launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "node",
            "request": "launch",
            "name": "debug webpack",
            "cwd":"${workspaceFolder}",
            "program":"${workspaceFolder}/node_modules/webpack-cli/bin/cli.js"
        }
    ]
}

2.2 webpack.cmd

• webpack-source\node_modules\.bin\webpack.cmd

• %~dp0是批处理文件所在的盘符:+路径(%~dp0 C:\vipdata\vipproject\webpack-source\node_modules.bin)

• SETLOCAL主要针对临时环境变量，不会影响到系统的变量环境设置，应与endlocal联用

• PATHEXT当在一个相同的目录结构下，有相同的多个主文件名，不同的文件后缀名时，系统会根据PATHEXT中的后缀名，选择其中顺序最靠前的那一个

@IF EXIST "%~dp0\node.exe" (//如果当前盘符的根目录下存在node.exe,用当前的node执行
  "%~dp0\node.exe"  "%~dp0\..\_webpack@4.39.3@webpack\bin\webpack.js" %*
) ELSE (//如果当前的盘符没有node.exe
  @SETLOCAL
  @SET PATHEXT=%PATHEXT:;.JS;=;%
  node  "%~dp0\..\_webpack@4.39.3@webpack\bin\webpack.js" %*
)

2.3 webpack.js

• node_modules\webpack\bin\webpack.js

const path = require("path");
const pkgPath = require.resolve(`${installedClis[0].package}/package.json`);
const pkg = require(pkgPath);
require(path.resolve(
    path.dirname(pkgPath),
    pkg.bin[installedClis[0].binName]
));

const path = require("path");
const pkgPath = require.resolve(`webpack-cli/package.json`);
const pkg = require(pkgPath);
require(path.resolve(path.dirname(pkgPath),pkg.bin['webpack-cli']));

npx webpack = node ./node_modules/webpack-cli/bin/cli.js

2.4 cli.js

const webpack = require("webpack");
const webpackOptions = require("./webpack.config");
const compiler = webpack(webpackOptions);
compiler.run((err, stats) => {
  console.log(err);
  console.log(stats.toJson({
    entries:true,
    chunks:true,
    modules:true,
    _modules:true,
    assets:true
  }));
});

3.Stats 对象

• 在 Webpack 的回调函数中会得到stats对象
• 这个对象实际来自于Compilation.getStats()，返回的是主要含有modules、chunks和assets三个属性值的对象。
• Stats对象本质上来自于lib/Stats.js的类实例

字段	含义
modules	记录了所有解析后的模块
chunks	记录了所有chunk
assets	记录了所有要生成的文件

npx webpack --profile --json > stats.json

{
  "errors": [],// 错误字符串 (error string) 的数组
  "warnings": [],//警告字符串 (warning string) 的数组
  "version": "4.39.3",// 用来编译的 webpack 的版本
  "hash": "3e945ec6b2c56d0b010e",//编译使用的 hash
  "time": 66, // 编译耗时 (ms)
  "builtAt": 1567225465347,//编译的时间
  "publicPath": "",//资源访问路径
  "outputPath": "C:\\vipdata\\vipproject\\webpack-source\\dist",//webpack输出目录
  "assetsByChunkName": {//用作映射的 chunk 的名称
    "lazy": "lazy.bundle.js",//chunk的名字叫lazy,lazy.bundle.js
    "main": "bundle.js"//chunk的名字叫main,打包出来了bundle.js
  },
  "assets": [//asset 对象 (asset objects) 的数组
    {
      "name": "bundle.js",//文件名
      "size": 9043,//大小
      "chunks": [//包含的代码块
        "main"
      ],
      "chunkNames": [//包含的代码块名称
        "main"
      ],
      "emitted": true//是否要生成
    },
    {
      "name": "lazy.bundle.js", // 输出的文件名
      "size": 336,// 文件的大小
      "chunks": [ // 这个 asset 包含的 chunk 的 id
        "lazy"
      ],
      "chunkNames": [// 这个 asset 包含的 chunk
        "lazy"
      ],
      "emitted": true  // 表示这个 asset 是否会让它输出到 output 目录
    }
  ],
  "filteredAssets": 0,
  "entrypoints": {
    "main": {
      "chunks": [
        "main"
      ],
      "assets": [
        "bundle.js"
      ],
      "children": {},
      "childAssets": {}
    }
  },
  "namedChunkGroups": {
    "main": {
      "chunks": [
        "main"
      ],
      "assets": [
        "bundle.js"
      ],
      "children": {},
      "childAssets": {}
    },
    "lazy": {
      "chunks": [
        "lazy"
      ],
      "assets": [
        "lazy.bundle.js"
      ],
      "children": {},
      "childAssets": {}
    }
  },
  "chunks": [ //chunk 对象 (chunk objects) 的数组
    {
      "id": "lazy", // 这个 chunk 的id
      "rendered": true,// 表示这个 chunk 是否会参与进编译
      "initial": false,
      "entry": false,// 表示这个 chunk 是否包含 webpack 的运行时
      "size": 24,//预估的模块大小
      "names": [// 包含在这个 chunk 内的 chunk 的名字的数组
        "lazy"
      ],
      "files": [
        "lazy.bundle.js"
      ],
      "hash": "d08a8b502d30324f81e1",
      "siblings": [],
      "parents": [// 父 chunk 的 ids
        "main"
      ],
      "children": [],
      "childrenByOrder": {},
      "modules": [
        {
          "id": "./src/lazy.js",
          "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\lazy.js",
          "name": "./src/lazy.js",
          "index": 2,
          "index2": 2,
          "size": 24,
          "cacheable": true,
          "built": true,
          "optional": false,
          "prefetched": false,
          "chunks": [
            "lazy"
          ],
          "issuer": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "issuerId": "./src/index.js",
          "issuerName": "./src/index.js",
          "issuerPath": [
            {
              "id": "./src/index.js",
              "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
              "name": "./src/index.js",
              "profile": {
                "factory": 18,
                "building": 14
              }
            }
          ],
          "profile": {
            "factory": 4,
            "building": 2
          },
          "failed": false,
          "errors": 0,
          "warnings": 0,
          "assets": [],
          "reasons": [// 生成 assets 的原因
            {
              "moduleId": "./src/index.js",//模块的ID
              "moduleIdentifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",//唯一标识
              "module": "./src/index.js",//模块
              "moduleName": "./src/index.js",//模块名称
              "type": "import()",//类型
              "userRequest": "./lazy",//用户请求方式
              "loc": "2:0-46"//在父模块中的位置
            }
          ],
          "providedExports": null,
          "optimizationBailout": [],
          "depth": 1,
          "source": "module.exports = 'lazy';"
        }
      ],
      "filteredModules": 0,
      "origins": [
        {
          "moduleId": "./src/index.js",// 模块的ID
          "module": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",// 模块的位置
          "moduleIdentifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",// 模块的地址
          "moduleName": "./src/index.js",//模块的相对地址
          "loc": "2:0-46",
          "request": "./lazy",
          "reasons": [] // 具体是哪行生成了这个chunk
        }
      ]
    },
    {
      "id": "main",
      "rendered": true,
      "initial": true,
      "entry": true,
      "size": 162,
      "names": [
        "main"
      ],
      "files": [
        "bundle.js"
      ],
      "hash": "263cadc0459e8470151b",
      "siblings": [],
      "parents": [],
      "children": [// 自己引用哪些chunk
        "lazy"
      ],
      "childrenByOrder": {}, // 引用的顺序
      "modules": [
        {
          "id": "./src/hello.js",
          "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\hello.js",
          "name": "./src/hello.js",
          "index": 1,
          "index2": 0,
          "size": 25,
          "cacheable": true,
          "built": true,
          "optional": false,
          "prefetched": false,
          "chunks": [
            "main"
          ],
          "issuer": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "issuerId": "./src/index.js",
          "issuerName": "./src/index.js",
          "issuerPath": [
            {
              "id": "./src/index.js",
              "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
              "name": "./src/index.js",
              "profile": {
                "factory": 18,
                "building": 14
              }
            }
          ],
          "profile": {
            "factory": 4,
            "building": 2
          },
          "failed": false,
          "errors": 0,
          "warnings": 0,
          "assets": [],
          "reasons": [
            {
              "moduleId": "./src/index.js",
              "moduleIdentifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
              "module": "./src/index.js",
              "moduleName": "./src/index.js",
              "type": "cjs require",
              "userRequest": "./hello",
              "loc": "1:12-30"
            }
          ],
          "providedExports": null,
          "optimizationBailout": [],
          "depth": 1,
          "source": "module.exports = 'hello';"
        },
        {
          "id": "./src/index.js",
          "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "name": "./src/index.js",
          "index": 0,
          "index2": 1,
          "size": 137,
          "cacheable": true,
          "built": true,
          "optional": false,
          "prefetched": false,
          "chunks": [
            "main"
          ],
          "issuer": null,
          "issuerId": null,
          "issuerName": null,
          "issuerPath": null,
          "profile": {
            "factory": 18,
            "building": 14
          },
          "failed": false,
          "errors": 0,
          "warnings": 0,
          "assets": [],
          "reasons": [
            {
              "moduleId": null,
              "moduleIdentifier": null,
              "module": null,
              "moduleName": null,
              "type": "single entry",
              "userRequest": "./src/index.js",
              "loc": "main"
            }
          ],
          "providedExports": null,
          "optimizationBailout": [],
          "depth": 0,
          "source": "let hello = require('./hello');\r\nimport(/* webpackChunkName: \"lazy\" */'./lazy').then(result=>{\r\n    console.log(hello,resut.default)\r\n});"
        }
      ],
      "filteredModules": 0,
      "origins": [
        {
          "module": "",
          "moduleIdentifier": "",
          "moduleName": "",
          "loc": "main",
          "request": "./src/index.js",
          "reasons": []
        }
      ]
    }
  ],
  "modules": [// 模块对象 (module objects) 的数组
    {
      "id": "./src/hello.js",//模块ID
      "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\hello.js",//webpack内部使用的唯一的标识
      "name": "./src/hello.js",// 实际文件的地址
      "index": 1,//索引
      "index2": 0,//索引
      "size": 25,// 预估模块的大小 (byte)
      "cacheable": true,// 表示这个模块是否会被缓存
      "built": true,// 表示这个模块会参与 Loaders , 解析, 并被编译
      "optional": false,// 每一个对这个模块的请求都会包裹在 `try... catch` 内
      "prefetched": false,// 表示这个模块是否会被 prefetched
      "chunks": [//此模块在哪个代码块内
        "main"
      ],
      "issuer": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",//使用者唯一标识
      "issuerId": "./src/index.js",//使用者ID
      "issuerName": "./src/index.js",//使用者名称
      "issuerPath": [//使用者路径
        {
          "id": "./src/index.js",
          "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "name": "./src/index.js",
          "profile": { //这个模块特有的编译时间数据(ms)
            "factory": 18,// 解决依赖的时间
            "building": 14 // 载入和解析的时间
          }
        }
      ],
      "profile": {
        "factory": 4,// 解决依赖的时间
        "building": 2// 载入和解析的时间
      },
      "failed": false,//是否失败
      "errors": 0,// 处理模块时错误的数量
      "warnings": 0,// 处理模块时警告的数量
      "assets": [],//在哪个资源内
      "reasons": [
        {
          "moduleId": "./src/index.js",// 模块的 ID
          "moduleIdentifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",// 模块的地址
          "module": "./src/index.js",// 所基于模块的相对地址 context
          "moduleName": "./src/index.js",
          "type": "cjs require",// 使用的请求的种类 (require或import)
          "userRequest": "./hello",// 用来 `import` 或者 `require` 的源字符串
          "loc": "1:12-30" // 导致这个被加入依赖图标的代码行数
        }
      ],
      "providedExports": null,//提供的导出对象
      "optimizationBailout": [],//失败时的优化
      "depth": 1,//模块深度
      "source": "module.exports = 'hello';"// 字符串化的输入
    },
    {
      "id": "./src/index.js",
      "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
      "name": "./src/index.js",
      "index": 0,
      "index2": 1,
      "size": 137,
      "cacheable": true,
      "built": true,
      "optional": false,
      "prefetched": false,
      "chunks": [
        "main"
      ],
      "issuer": null,
      "issuerId": null,
      "issuerName": null,
      "issuerPath": null,
      "profile": {
        "factory": 18,
        "building": 14
      },
      "failed": false,
      "errors": 0,
      "warnings": 0,
      "assets": [],
      "reasons": [
        {
          "moduleId": null,
          "moduleIdentifier": null,
          "module": null,
          "moduleName": null,
          "type": "single entry",
          "userRequest": "./src/index.js",
          "loc": "main"
        }
      ],
      "providedExports": null,
      "optimizationBailout": [],
      "depth": 0,
      "source": "let hello = require('./hello');\r\nimport(/* webpackChunkName: \"lazy\" */'./lazy').then(result=>{\r\n    console.log(hello,resut.default)\r\n});"
    },
    {
      "id": "./src/lazy.js",
      "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\lazy.js",
      "name": "./src/lazy.js",
      "index": 2,
      "index2": 2,
      "size": 24,
      "cacheable": true,
      "built": true,
      "optional": false,
      "prefetched": false,
      "chunks": [
        "lazy"
      ],
      "issuer": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
      "issuerId": "./src/index.js",
      "issuerName": "./src/index.js",
      "issuerPath": [
        {
          "id": "./src/index.js",
          "identifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "name": "./src/index.js",
          "profile": {
            "factory": 18,
            "building": 14
          }
        }
      ],
      "profile": {
        "factory": 4,
        "building": 2
      },
      "failed": false,
      "errors": 0,
      "warnings": 0,
      "assets": [],
      "reasons": [
        {
          "moduleId": "./src/index.js",
          "moduleIdentifier": "C:\\vipdata\\vipproject\\webpack-source\\src\\index.js",
          "module": "./src/index.js",
          "moduleName": "./src/index.js",
          "type": "import()",
          "userRequest": "./lazy",
          "loc": "2:0-46"
        }
      ],
      "providedExports": null,
      "optimizationBailout": [],
      "depth": 1,
      "source": "module.exports = 'lazy';"
    }
  ],
  "filteredModules": 0,
  "logging": {
    "webpack.buildChunkGraph.visitModules": {
      "entries": [],
      "filteredEntries": 5,
      "debug": false
    }
  },
  "children": []
}

4. 详细工作流程

webpackcode