• 关于webpack(v5.74.0)的模块联邦原理

    在webpack中模块联邦的实现主要依赖于两个插件ContainerReferencePlugin和ContainerPlugin，ContainerPlugin是用来添加入口依赖并给当前依赖添加异步依赖，ContainerReferencePlugin用来添加解析用户的请求并分析是否是远程模块，然后加载远程模块。接下来我们看看源码是如何实现的。

    基础配置

    const path = require('path');
const { ModuleFederationPlugin } = require("webpack").container;

module.exports = {
	mode: 'development',
	plugins: [
		new ModuleFederationPlugin({
      // 指定导出的容器名称
      name: "app_exposes",
			library:{ type: "var", name: "app_exposes" },
      // 打包生成的文件名称
      filename: "remoteEntry.js",
      // 导出对应的模块
      exposes: {
        "./math": "./src/math.js",
      },
    })
	],
	entry: './src/index.js',
	output: {
		filename: 'bundle.js',
		path: path.resolve(__dirname, 'dist'),
		clean:true
	},
};


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    ContainerPlugin

    const ContainerPlugin = require('./ContainerPlugin')
class TestPlugin {
  constructor(options) {
    this._options = options
  }
  apply(compiler) {
    const options = this._options
    // 添加当前允许的变量挂载类型window,var,self,this去接收__webpack_exports__
    compiler.options.output.enabledLibraryTypes.push(options.library.type)
    // 在初始化内部插件集合完成设置之后调用
    compiler.hooks.afterPlugins.tap("TestPlugin", () => {
      new ContainerPlugin({
        name: options.name,
        library:options.library,
        filename: options.filename,
        runtime: options.runtime,
        exposes: options.exposes
      }).apply(compiler);
    });
  }
}

module.exports = TestPlugin

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    主要执行了ContainerPlugin插件：

    class ContainerPlugin {
	/**
	 * @param {ContainerPluginOptions} options options
	 */
	constructor(options) {
		this._options = {
			name: options.name,
			shareScope: options.shareScope || "default",
			// 全局变量接收__webpack_exports__
			library: options.library || {
				type: "var",
				name: options.name
			},
			runtime: options.runtime,
			filename: options.filename || undefined,
			exposes: parseOptions(
				options.exposes,
				item => ({
					import: Array.isArray(item) ? item : [item],
					name: undefined
				}),
				item => ({
					import: Array.isArray(item.import) ? item.import : [item.import],
					name: item.name || undefined
				})
			)
		};
	}

	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const { name, exposes, shareScope, filename, library, runtime } =
			this._options;

		compiler.options.output.enabledLibraryTypes.push(library.type);

		compiler.hooks.make.tapAsync(PLUGIN_NAME, (compilation, callback) => {
			const dep = new ContainerEntryDependency(name, exposes, shareScope);
			dep.loc = { name };
			compilation.addEntry(
				compilation.options.context,
				dep,
				{
					name,
					filename,// 输出的文件名
					runtime,
					library
				},
				error => {
					if (error) return callback(error);
					callback();
				}
			);
		});

		compiler.hooks.thisCompilation.tap(
			PLUGIN_NAME,
			(compilation, { normalModuleFactory }) => {
				// 设置remoteEntry.js的依赖和创造remoteEntry的工厂
				compilation.dependencyFactories.set(
					ContainerEntryDependency,
					new ContainerEntryModuleFactory()// ContainerEntryModule 依赖ContainerExposedDependency
				);
				// 设置依赖的模块创造工厂
				compilation.dependencyFactories.set(
					ContainerExposedDependency,// math
					normalModuleFactory // 普通模块
				);
			}
		);
	}
}

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    可以看出通过addEntry方法添加了一个入口，并设置了依赖ContainerEntryDependency，然后在thisCompilation中设置了ContainerEntryDependency依赖的创造模块工厂ContainerEntryModuleFactory。也就意味着会先调用ContainerEntryModuleFactory函数的ContainerEntryModule去生成模块。

    module.exports = class ContainerEntryModuleFactory extends ModuleFactory {
	/**
	 * @param {ModuleFactoryCreateData} data data object
	 * @param {function(Error=, ModuleFactoryResult=): void} callback callback
	 * @returns {void}
	 */
	create({ dependencies: [dependency] }, callback) {
		const dep = /** @type {ContainerEntryDependency} */ (dependency);
		callback(null, {
			module: new ContainerEntryModule(dep.name, dep.exposes, dep.shareScope)
		});
	}
};

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    我们重点看ContainerEntryModule方法的build方法和codeGeneration方法。

    /** 给当前模块添加依赖，设置变量
 * @param {WebpackOptions} options webpack options
 * @param {Compilation} compilation the compilation
 * @param {ResolverWithOptions} resolver the resolver
 * @param {InputFileSystem} fs the file system
 * @param {function(WebpackError=): void} callback callback function
 * @returns {void}
 */
build(options, compilation, resolver, fs, callback) {
	this.buildMeta = {};
	// 设置三个变量
	this.buildInfo = {
		strict: true,
		topLevelDeclarations: new Set(["moduleMap", "get", "init"])
	};
	this.buildMeta.exportsType = "namespace";

	this.clearDependenciesAndBlocks();
	// remoteEntry.js依赖于main.js，此时AsyncDependenciesBlock表示公开模块来创建一个额外的容器入口。客户端会通过jsonp加载
	for (const [name, options] of this._exposes) {
		// 添加异步模块
		const block = new AsyncDependenciesBlock(
			{
				name: options.name
			},
			{ name },
			options.import[options.import.length - 1]
		);
		let idx = 0;
		for (const request of options.import) {
			// name=math.js
			const dep = new ContainerExposedDependency(name, request);
			dep.loc = {
				name,
				index: idx++
			};
			// build过程中设置异步模块的依赖（ContainerExposedDependency）
			block.addDependency(dep);
		}
		// 添加异步模块，会把math.js单独打包出来，同时会在remoteEntry.js文件中引入运行时的代码
		this.addBlock(block);
	}
	// 设置导出依赖
	this.addDependency(new StaticExportsDependency(["get", "init"], false));

	callback();
}

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    在执行build方法过程中会给remoteEntry模块添加一个异步依赖math.js。再来看看codeGeneration执行过程：

    /**
 * @param {CodeGenerationContext} context context for code generation
 * @returns {CodeGenerationResult} result
 */
codeGeneration({ moduleGraph, chunkGraph, runtimeTemplate }) {
	const sources = new Map();
	const runtimeRequirements = new Set([
		// __webpack_require__.d 
		RuntimeGlobals.definePropertyGetters,
		// __webpack_require__.o
		RuntimeGlobals.hasOwnProperty,
		// __webpack_exports__
		RuntimeGlobals.exports
	]);
	const getters = [];
	// 给webpack/container/entry/app_exposes模块新增'"./math": () => {\n\treturn __webpack_require__.e("src_math_js").then(() => (() => ((__webpack_require__(/*! ./src/math.js */ "./src/math.js")))));\n}'
	for (const block of this.blocks) {
		const { dependencies } = block;
		// 取出异步模块
		const modules = dependencies.map(dependency => {
			const dep = /** @type {ContainerExposedDependency} */ (dependency);
			return {
				name: dep.exposedName,
				module: moduleGraph.getModule(dep),
				request: dep.userRequest
			};
		});

		let str;
		// 获取要请求的模块
		if (modules.some(m => !m.module)) {
			str = runtimeTemplate.throwMissingModuleErrorBlock({
				request: modules.map(m => m.request).join(", ")
			});
		} else {
			// runtimeTemplate.blockPromise=>__webpack_require__.e
			str = `return ${runtimeTemplate.blockPromise({
				block,
				message: "",
				chunkGraph,
				runtimeRequirements
				// runtimeTemplate.returningFunction  () => ()
			})}.then(${runtimeTemplate.returningFunction(
				runtimeTemplate.returningFunction(
					`(${modules
						.map(({ module, request }) =>
						// runtimeTemplate.moduleRaw =>__webpack_require__(/*! ./src/math.js */ "./src/math.js")
							runtimeTemplate.moduleRaw({
								module,
								chunkGraph,
								request,
								weak: false,
								runtimeRequirements
							})
						)
						.join(", ")})`
				)
			)});`;
		}

		getters.push(
			`${JSON.stringify(modules[0].name)}: ${runtimeTemplate.basicFunction(
				"",
				[str]
			)}`
		);
	}
	// remoteEntry.js文件的内容
	const source = Template.asString([
		`var moduleMap = {`,
		Template.indent(getters.join(",\n")),
		"};",
		// 定义remotEntry.js的get
		`var get = ${runtimeTemplate.basicFunction("module, getScope", [
			`${RuntimeGlobals.currentRemoteGetScope} = getScope;`,
			// reusing the getScope variable to avoid creating a new var (and module is also used later)
			"getScope = (",
			Template.indent([
				`${RuntimeGlobals.hasOwnProperty}(moduleMap, module)`,
				Template.indent([
					"? moduleMap[module]()",
					`: Promise.resolve().then(${runtimeTemplate.basicFunction(
						"",
						"throw new Error('Module \"' + module + '\" does not exist in container.');"
					)})`
				])
			]),
			");",
			`${RuntimeGlobals.currentRemoteGetScope} = undefined;`,
			"return getScope;"
		])};`,
		// 定义remotEntry.js的init
		`var init = ${runtimeTemplate.basicFunction("shareScope, initScope", [
			`if (!${RuntimeGlobals.shareScopeMap}) return;`,
			`var name = ${JSON.stringify(this._shareScope)}`,
			`var oldScope = ${RuntimeGlobals.shareScopeMap}[name];`,
			`if(oldScope && oldScope !== shareScope) throw new Error("Container initialization failed as it has already been initialized with a different share scope");`,
			`${RuntimeGlobals.shareScopeMap}[name] = shareScope;`,
			`return ${RuntimeGlobals.initializeSharing}(name, initScope);`
		])};`,
		"",
		"// This exports getters to disallow modifications",
		`${RuntimeGlobals.definePropertyGetters}(exports, {`,
		Template.indent([
			`get: ${runtimeTemplate.returningFunction("get")},`,
			`init: ${runtimeTemplate.returningFunction("init")}`
		]),
		"});"
	]);

	sources.set(
		"javascript",
		this.useSourceMap || this.useSimpleSourceMap
			? new OriginalSource(source, "webpack/container-entry")
			: new RawSource(source)
	);

	return {
		sources,
		// remotentry添加运行时函数
		runtimeRequirements
	};
}

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    这里主要是设置remoteEntry.js中的webpack/container/entry/app_exposes模块内容：

    var moduleMap = {
  "./math": () => {
    return __webpack_require__
      .e("src_math_js")
      .then(
        () => () => __webpack_require__(/*! ./src/math.js */ "./src/math.js")
      );
  },
};
var get = (module, getScope) => {
  __webpack_require__.R = getScope;
  getScope = __webpack_require__.o(moduleMap, module)
    ? moduleMap[module]()
    : Promise.resolve().then(() => {
        throw new Error('Module "' + module + '" does not exist in container.');
      });
  __webpack_require__.R = undefined;
  return getScope;
};
var init = (shareScope, initScope) => {
  if (!__webpack_require__.S) return;
  var name = "default";
  var oldScope = __webpack_require__.S[name];
  if (oldScope && oldScope !== shareScope)
    throw new Error(
      "Container initialization failed as it has already been initialized with a different share scope"
    );
  __webpack_require__.S[name] = shareScope;
  return __webpack_require__.I(name, initScope);
};

// This exports getters to disallow modifications
__webpack_require__.d(exports, {
  get: () => get,
  init: () => init,
});

//# sourceURL=webpack://webpack/container_entry?

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    此时我们打包一下：
    在这里插入图片描述
    会生成三个文件，bundle.js文件就是我们配置的entry文件入口。在这里插入图片描述
    remoteEntry.js文件是我们新增加的入口，webpack/container/entry/app_exposes依赖就是此处的dep.。在这里插入图片描述

    在这里插入图片描述
    math.js文件是remoteEntry.js文件中webpack/container/entry/app_exposes的依赖。该依赖的添加是在webpack/container/entry/app_exposes模块的build阶段：
    在这里插入图片描述
    此时ContainerPlugin插件做的事情我们就分析清楚了。接下来分析ContainerReferencePlugin插件。

    ContainerReferencePlugin

    基础配置

    const path = require('path');

module.exports = {
  mode: 'development',
  plugins: [
    new ModuleFederationPlugin({
      // 引用的外部资源列表
      remotes: {
        app_exposes: 'app_exposes@http://localhost:8081/remoteEntry.js',
      }
    })
  ],
  entry: './src/index2.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist'),
    clean: true
  },
};

// index2.js
import('app_exposes/math')

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    主要执行的是ModuleFederationPlugin插件：

    /*
  MIT License http://www.opensource.org/licenses/mit-license.php
  Author Tobias Koppers @sokra and Zackary Jackson @ScriptedAlchemy
*/

"use strict";

const ContainerReferencePlugin = require("./ContainerReferencePlugin");

class ModuleFederationPlugin {
  /**
   * @param {ModuleFederationPluginOptions} options options
   */
  constructor(options) {

    this._options = options;
  }

  /**
   * Apply the plugin
   * @param {Compiler} compiler the compiler instance
   * @returns {void}
   */
  apply(compiler) {
    const { _options: options } = this;
    const library = { type: "var", name: options.name };
    const remoteType = "script";
    compiler.options.output.enabledLibraryTypes.push(library.type);
    compiler.hooks.afterPlugins.tap("ModuleFederationPlugin", () => {
      new ContainerReferencePlugin({
        remoteType,
        remotes: options.remotes
      }).apply(compiler);
    });
  }
}

module.exports = ModuleFederationPlugin;

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    该插件主要执行ContainerReferencePlugin插件，我们继续看：

    /*
  MIT License http://www.opensource.org/licenses/mit-license.php
  Author Tobias Koppers @sokra and Zackary Jackson @ScriptedAlchemy
*/

"use strict";

const ExternalsPlugin = require("webpack/lib/ExternalsPlugin");
const RuntimeGlobals = require("webpack/lib/RuntimeGlobals");
const FallbackDependency = require("webpack/lib/container/FallbackDependency");
const FallbackItemDependency = require("webpack/lib/container/FallbackItemDependency");
const FallbackModuleFactory = require("webpack/lib/container/FallbackModuleFactory");
const RemoteModule = require("webpack/lib/container/RemoteModule");
const RemoteRuntimeModule = require("webpack/lib/container/RemoteRuntimeModule");
const RemoteToExternalDependency = require("webpack/lib/container/RemoteToExternalDependency");
const { parseOptions } = require("webpack/lib/container/options");



const slashCode = "/".charCodeAt(0);

class ContainerReferencePlugin {
  /**
   * @param {ContainerReferencePluginOptions} options options
   */
  constructor(options) {
    this._remoteType = options.remoteType;
    this._remotes = parseOptions(
      options.remotes,
      item => ({
        external: Array.isArray(item) ? item : [item],
        shareScope: options.shareScope || "default"
      }),
      item => ({
        external: Array.isArray(item.external)
          ? item.external
          : [item.external],
        shareScope: item.shareScope || options.shareScope || "default"
      })
    );
  }

  /** 1. 定义了普通模块
   * Apply the plugin
   * @param {Compiler} compiler the compiler instance
   * @returns {void}
   */
  apply(compiler) {
    const { _remotes: remotes, _remoteType: remoteType } = this;

    /** @type {Record} */
    const remoteExternals = {};
    for (const [key, config] of remotes) {
      let i = 0;
      for (const external of config.external) {
        if (external.startsWith("internal ")) continue;
        remoteExternals[
          `webpack/container/reference/${key}${i ? `/fallback-${i}` : ""}`
        ] = external;
        i++;
      }
    }
    // ExternalModuleFactoryPlugin=>ExternalModule最终返回webpack/container/reference/app_exposes的模块内容
    new ExternalsPlugin(remoteType, remoteExternals).apply(compiler);

    compiler.hooks.compilation.tap(
      "ContainerReferencePlugin",
      (compilation, { normalModuleFactory }) => {
        // 
        compilation.dependencyFactories.set(
          RemoteToExternalDependency,
          normalModuleFactory
        );
        // 定义了普通模块
        compilation.dependencyFactories.set(
          FallbackItemDependency,
          normalModuleFactory
        );
        // 当前模块依赖于FallbackDependency
        compilation.dependencyFactories.set(
          FallbackDependency,
          new FallbackModuleFactory() // FallbackModule依赖于FallbackItemDependency
        );
        // 4. 第一次解析(type=module)'./src/index2.js' 第二次'app_exposes/math'
        normalModuleFactory.hooks.factorize.tap(
          "ContainerReferencePlugin",
          data => {
            if (!data.request.includes("!")) {
              for (const [key, config] of remotes) {
                // 在解析依赖的时候如果以app_exposes开头并且有'\'
                if (
                  data.request.startsWith(`${key}`) &&
                  (data.request.length === key.length ||
                    data.request.charCodeAt(key.length) === slashCode)
                ) {
                  // app_exposes/math依赖于RemoteToExternalDependency 
                  return new RemoteModule(
                    data.request,
                    config.external.map((external, i) =>
                      external.startsWith("internal ")
                        ? external.slice(9)
                        : `webpack/container/reference/${key}${i ? `/fallback-${i}` : ""
                        }`
                    ),
                    `.${data.request.slice(key.length)}`,
                    config.shareScope
                  );
                }
              }
            }
          }
        );
        // 添加运行时代码
        compilation.hooks.runtimeRequirementInTree
          .for(RuntimeGlobals.ensureChunkHandlers)
          .tap("ContainerReferencePlugin", (chunk, set) => {
            set.add(RuntimeGlobals.module);
            set.add(RuntimeGlobals.moduleFactoriesAddOnly);
            set.add(RuntimeGlobals.hasOwnProperty);
            set.add(RuntimeGlobals.initializeSharing);
            set.add(RuntimeGlobals.shareScopeMap);
            compilation.addRuntimeModule(chunk, new RemoteRuntimeModule());
          });
      }
    );
  }
}

module.exports = ContainerReferencePlugin;

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    首先执行的是ExternalsPlugin插件，其次执行的compiler.hooks.compilation.tap回调方法。compiler.hooks.compilation.tap主要设置了FallbackDependency依赖的模块创造函数，其次监听了normalModuleFactory.hooks.factorize钩子，该钩子是在解析依赖路径的时候会触发。我们在来看看ExternalsPlugin插件干啥了。

    /*
  MIT License http://www.opensource.org/licenses/mit-license.php
  Author Tobias Koppers @sokra
*/

"use strict";

const ExternalModuleFactoryPlugin = require("./ExternalModuleFactoryPlugin");

/** @typedef {import("../declarations/WebpackOptions").Externals} Externals */
/** @typedef {import("./Compiler")} Compiler */

class ExternalsPlugin {
  /**
   * @param {string | undefined} type default external type
   * @param {Externals} externals externals config
   */
  constructor(type, externals) {
    this.type = type;
    this.externals = externals;
  }

  /** compile先于compilation执行
   * Apply the plugin
   * @param {Compiler} compiler the compiler instance
   * @returns {void}
   */
  apply(compiler) {// beforeCompile 之后立即调用，但在一个新的 compilation 创建之前
    compiler.hooks.compile.tap("ExternalsPlugin", ({ normalModuleFactory }) => {
      new ExternalModuleFactoryPlugin(this.type, this.externals).apply(
        normalModuleFactory
      );
    });
  }
}

module.exports = ExternalsPlugin;

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    主要执行ExternalModuleFactoryPlugin插件：

    ...

class ExternalModuleFactoryPlugin {
  /**
   * @param {string | undefined} type default external type
   * @param {Externals} externals externals config
   */
  constructor(type, externals) {
    this.type = type;
    this.externals = externals;
  }

  /**
   * @param {NormalModuleFactory} normalModuleFactory the normal module factory
   * @returns {void}
   */
  apply(normalModuleFactory) {
    const globalType = this.type;// 2.第一次解析(type=module)'./src/index2.js',3.第二次解析（type=module）'app_exposes/math',6.第三次解析(type=module)'webpack/container/reference/app_exposes' 第四次解析(type=script)'webpack/container/reference/app_exposes'
    normalModuleFactory.hooks.factorize.tapAsync(
      "ExternalModuleFactoryPlugin",
      (data, callback) => {
        const context = data.context;
        const contextInfo = data.contextInfo;
        const dependency = data.dependencies[0];
        const dependencyType = data.dependencyType;

        /** value 'app_exposes@http://localhost:8081/remoteEntry.js'
         * @param {string|string[]|boolean|Record} value the external config
         * @param {string|undefined} type type of external
         * @param {function(Error=, ExternalModule=): void} callback callback
         * @returns {void}
         */
        const handleExternal = (value, type, callback) => {
          if (value === false) {
            // Not externals, fallback to original factory
            return callback();
          }
          /** @type {string | string[] | Record} */
          let externalConfig;
          if (value === true) {
            externalConfig = dependency.request;
          } else {
            externalConfig = value;
          }
          // When no explicit type is specified, extract it from the externalConfig
          if (type === undefined) {
            if (
              typeof externalConfig === "string" &&
              UNSPECIFIED_EXTERNAL_TYPE_REGEXP.test(externalConfig)
            ) {
              const idx = externalConfig.indexOf(" ");
              type = externalConfig.slice(0, idx);
              externalConfig = externalConfig.slice(idx + 1);
            } else if (
              Array.isArray(externalConfig) &&
              externalConfig.length > 0 &&
              UNSPECIFIED_EXTERNAL_TYPE_REGEXP.test(externalConfig[0])
            ) {
              const firstItem = externalConfig[0];
              const idx = firstItem.indexOf(" ");
              type = firstItem.slice(0, idx);
              externalConfig = [
                firstItem.slice(idx + 1),
                ...externalConfig.slice(1)
              ];
            }
          }
          callback(
            null,
            new ExternalModule(// 8.最终执行
              externalConfig,
              type || globalType,
              dependency.request
            )
          );
        };

        /**
         * @param {Externals} externals externals config
         * @param {function((Error | null)=, ExternalModule=): void} callback callback
         * @returns {void}
         */
        const handleExternals = (externals, callback) => {
          if (typeof externals === "string") {
            if (externals === dependency.request) {
              return handleExternal(dependency.request, undefined, callback);
            }
          } else if (Array.isArray(externals)) {
            let i = 0;
            const next = () => {
              let asyncFlag;
              const handleExternalsAndCallback = (err, module) => {
                if (err) return callback(err);
                if (!module) {
                  if (asyncFlag) {
                    asyncFlag = false;
                    return;
                  }
                  return next();
                }
                callback(null, module);
              };

              do {
                asyncFlag = true;
                if (i >= externals.length) return callback();
                handleExternals(externals[i++], handleExternalsAndCallback);
              } while (!asyncFlag);
              asyncFlag = false;
            };

            next();
            return;
          } else if (externals instanceof RegExp) {
            if (externals.test(dependency.request)) {
              return handleExternal(dependency.request, undefined, callback);
            }
          } else if (typeof externals === "function") {
            const cb = (err, value, type) => {
              if (err) return callback(err);
              if (value !== undefined) {
                handleExternal(value, type, callback);
              } else {
                callback();
              }
            };
            if (externals.length === 3) {
              // TODO webpack 6 remove this
              callDeprecatedExternals(
                externals,
                context,
                dependency.request,
                cb
              );
            } else {
              const promise = externals(
                {
                  context,
                  request: dependency.request,
                  dependencyType,
                  contextInfo,
                  getResolve: options => (context, request, callback) => {
                    const resolveContext = {
                      fileDependencies: data.fileDependencies,
                      missingDependencies: data.missingDependencies,
                      contextDependencies: data.contextDependencies
                    };
                    let resolver = normalModuleFactory.getResolver(
                      "normal",
                      dependencyType
                        ? cachedSetProperty(
                          data.resolveOptions || EMPTY_RESOLVE_OPTIONS,
                          "dependencyType",
                          dependencyType
                        )
                        : data.resolveOptions
                    );
                    if (options) resolver = resolver.withOptions(options);
                    if (callback) {
                      resolver.resolve(
                        {},
                        context,
                        request,
                        resolveContext,
                        callback
                      );
                    } else {
                      return new Promise((resolve, reject) => {
                        resolver.resolve(
                          {},
                          context,
                          request,
                          resolveContext,
                          (err, result) => {
                            if (err) reject(err);
                            else resolve(result);
                          }
                        );
                      });
                    }
                  }
                },
                cb
              );
              if (promise && promise.then) promise.then(r => cb(null, r), cb);
            }
            return;// {webpack/container/reference/app_exposes: 'app_exposes@http://localhost:8081/remoteEntry.js'}
          } else if (typeof externals === "object") {
            const resolvedExternals = resolveLayer(
              externals,
              contextInfo.issuerLayer
            );
            if (
              Object.prototype.hasOwnProperty.call(
                resolvedExternals,
                dependency.request
              )
            ) {// 7.最终执行
              return handleExternal(
                resolvedExternals[dependency.request],
                undefined,
                callback
              );
            }
          }
          callback();
        };

        handleExternals(this.externals, callback);
      }
    );
  }
}
module.exports = ExternalModuleFactoryPlugin;

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    该插件主要执行normalModuleFactory.hooks.factorize监听解析路径，主要是用来处理webpack/container/reference/app_exposes依赖，最终执行ExternalModule模块。我们看看ExternalModule模块返回了什么内容。

    const getSourceForScriptExternal = (urlAndGlobal, runtimeTemplate) => {
  if (typeof urlAndGlobal === "string") {
    urlAndGlobal = extractUrlAndGlobal(urlAndGlobal);
  }// 'http://localhost:8081/remoteEntry.js'
  const url = urlAndGlobal[0];
  const globalName = urlAndGlobal[1];
  return {
    init: "var __webpack_error__ = new Error();",
    expression: `new Promise(${runtimeTemplate.basicFunction(
      "resolve, reject",
      [
        `if(typeof ${globalName} !== "undefined") return resolve();`,
        `${RuntimeGlobals.loadScript}(${JSON.stringify(
          url
        )}, ${runtimeTemplate.basicFunction("event", [
          `if(typeof ${globalName} !== "undefined") return resolve();`,
          "var errorType = event && (event.type === 'load' ? 'missing' : event.type);",
          "var realSrc = event && event.target && event.target.src;",
          "__webpack_error__.message = 'Loading script failed.\\n(' + errorType + ': ' + realSrc + ')';",
          "__webpack_error__.name = 'ScriptExternalLoadError';",
          "__webpack_error__.type = errorType;",
          "__webpack_error__.request = realSrc;",
          "reject(__webpack_error__);"
        ])}, ${JSON.stringify(globalName)});`
      ]
    )}).then(${runtimeTemplate.returningFunction(
      `${globalName}${propertyAccess(urlAndGlobal, 2)}`
    )})`,
    runtimeRequirements: RUNTIME_REQUIREMENTS_FOR_SCRIPT
  };
};

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    打包后生成：

    /***/ "webpack/container/reference/app_exposes":
/*!*******************************************************************!*\
  !*** external "app_exposes@http://localhost:8081/remoteEntry.js" ***!
  \*******************************************************************/
/***/ ((module, __unused_webpack_exports, __webpack_require__) => {

"use strict";
var __webpack_error__ = new Error();
module.exports = new Promise((resolve, reject) => {
	// 已有全局变量app_exposes说明已加载
	if(typeof app_exposes !== "undefined") return resolve();
	__webpack_require__.l("http://localhost:8081/remoteEntry.js", (event) => {
		if(typeof app_exposes !== "undefined") return resolve();
		var errorType = event && (event.type === 'load' ? 'missing' : event.type);
		var realSrc = event && event.target && event.target.src;
		__webpack_error__.message = 'Loading script failed.\n(' + errorType + ': ' + realSrc + ')';
		__webpack_error__.name = 'ScriptExternalLoadError';
		__webpack_error__.type = errorType;
		__webpack_error__.request = realSrc;
		reject(__webpack_error__);
	}, "app_exposes");
}).then(() => (app_exposes));

/***/ })

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    可以看出是请求远程的remoteEntry.js模块。我们再来看看解析app_exposes/math的时候是怎么处理的。当解析app_expose/math路径的时候会执行返回RemoteModule模块内容。
    在这里插入图片描述
    我们重点看RemoteModule模块生成内容：

    build(options, compilation, resolver, fs, callback) {
    this.buildMeta = {};
    this.buildInfo = {
      strict: true
    };
    // 5. 添加'webpack/container/reference/app_exposes'依赖会触发normalModuleFactory.hooks.factorize
    this.clearDependenciesAndBlocks();
    if (this.externalRequests.length === 1) {
      this.addDependency(
        new RemoteToExternalDependency(this.externalRequests[0])
      );
    } else {
      this.addDependency(new FallbackDependency(this.externalRequests));
    }

    callback();
  }

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    该模块添加了webpack/container/reference/app_exposes依赖。再来看看codeGeneration返回：

    codeGeneration({ runtimeTemplate, moduleGraph, chunkGraph }) {
    const module = moduleGraph.getModule(this.dependencies[0]);
    const id = module && chunkGraph.getModuleId(module);// 'webpack/container/reference/app_exposes'
    const sources = new Map();
    sources.set("remote", new RawSource(""));
    const data = new Map();//shareScope = 'default' init=initExternal("webpack/container/reference/app_exposes")
    data.set("share-init", [
      {
        shareScope: this.shareScope,// 作为ShareRuntimeModule的switch的default
        initStage: 20,
        init: id === undefined ? "" : `initExternal(${JSON.stringify(id)});`
      }
    ]);
    return { sources, data, runtimeRequirements: RUNTIME_REQUIREMENTS };
  }

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    设置了data的share-init。重点看init方法，initExternal(${JSON.stringify(id)})主要是用来初始化模块内容。会被应用到__webpack_require__.I的switch方法中。
    在这里插入图片描述
    至此该插件实现的过程完毕。

    总结

    模块联邦功能实现主要依赖两个插件：

    1. ContainerPlugin
      首先新增入口，并给该chunk添加依赖ContainerEntryDependency（remoteEntry.js），remoteEntry模块build过程中添加一个异步模块math.js。
    2. ContainerReferencePlugin
      通过normalModuleFactory.hooks.factorize监听依赖解析，当解析app_exposes/math时会返回执行RemoteModule模块的build方法添加依赖webpack/container/reference/app_exposes，在code生成时设置initExternal方法。在解析webpack/container/reference/app_exposes依赖的时候会触发ExternalsPlugin插件的normalModuleFactory.hooks.factorize回调方法。主要返回ExternalModule模块内容(获取需要的远端模块内容)。
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  • 原文地址：https://blog.csdn.net/qq_35094120/article/details/127961314