webpack.js小尾巴

const webpack = (options, callback) => {
    //... 
    if (callback) {
        if (typeof callback !== "function") {
            throw new Error("Invalid argument: callback");
        }
        if (
            options.watch === true ||
            (Array.isArray(options) && options.some(o => o.watch))
        ) {
            const watchOptions = Array.isArray(options)
                ? options.map(o => o.watchOptions || {})
                : options.watchOptions || {};
            return compiler.watch(watchOptions, callback);
        }
        compiler.run(callback);
    }
    return compiler;
}

最终返回了compiler

  
exports.version = version;

// ...属性挂载,把引入的函数模块全部暴露出来
webpack.WebpackOptionsDefaulter = WebpackOptionsDefaulter;
webpack.WebpackOptionsApply = WebpackOptionsApply;
webpack.Compiler = Compiler;
webpack.MultiCompiler = MultiCompiler;
webpack.NodeEnvironmentPlugin = NodeEnvironmentPlugin;
// @ts-ignore Global @this directive is not supported
webpack.validate = validateSchema.bind(this, webpackOptionsSchema);
webpack.validateSchema = validateSchema;
webpack.WebpackOptionsValidationError = WebpackOptionsValidationError;

下面暴露了一些插件

const exportPlugins = (obj, mappings) => {
    for (const name of Object.keys(mappings)) {
        Object.defineProperty(obj, name, {
            configurable: false,
            enumerable: true,
            get: mappings[name]
        });
    }
};

exportPlugins(exports, {
    AutomaticPrefetchPlugin: () => require("./AutomaticPrefetchPlugin"),
    BannerPlugin: () => require("./BannerPlugin"),
    CachePlugin: () => require("./CachePlugin")}
)

再通俗一点的解释：

比如当你api.AutomaticPrefetchPlugin你能
调用AutomaticPrefetchPlugin文件下的方法

这个和上面的不同在于上面的是挂在webpack函数对象上的

Compiler.js正题

要想理解Compiler.js
必须要理解tapable
再写一遍 git地址

我们先简单的理解它为一个通过tap 注册插件
call是run插件的事件流，里面还有一些异步的操作

Compiler整理如下

class Compiler extends Tapable {
    constructor(context) {
        super();
        this.hooks = {
            //罗列一些出现频率比较高的
            shouldEmit: new SyncBailHook(["compilation"]),
            done: new AsyncSeriesHook(["stats"]),
            beforeRun: new AsyncSeriesHook(["compiler"]),
            run: new AsyncSeriesHook(["compiler"]),
            emit: new AsyncSeriesHook(["compilation"]),
            afterEmit: new AsyncSeriesHook(["compilation"]),
            thisCompilation: new SyncHook(["compilation", "params"]),
            compilation: new SyncHook(["compilation", "params"]),
            beforeCompile: new AsyncSeriesHook(["params"]),
            compile: new SyncHook(["params"]),
            make: new AsyncParallelHook(["compilation"]),
            afterCompile: new AsyncSeriesHook(["compilation"]),
            watchRun: new AsyncSeriesHook(["compiler"]),
            //...
            
        }
        // 添加事件流
        this._pluginCompat.tap("Compiler", options => {
            switch (options.name) {
                case "additional-pass":
                case "before-run":
                case "run":
                case "emit":
                case "after-emit":
                case "before-compile":
                case "make":
                case "after-compile":
                case "watch-run":
                    options.async = true;
                    break;
            }
        });
        
    }
    watch(){
           //...
    }
    
    run(callback) {
        //... 
    }
    // 清除输入文件系统
    purgeInputFileSystem() {
        if (this.inputFileSystem && this.inputFileSystem.purge) {
            this.inputFileSystem.purge();
        }
    }
    emitAssets(compilation, callback) {
        //...
    }
    createChildCompiler(
        compilation,
        compilerName,
        compilerIndex,
        outputOptions,
        plugins
    ) {
        //...
    
        
    }
    //...
    compile(callback){
        //...
    }    
}

和tapable用法一个模子里刻出来的，我们仔细的研究run函数

compiler.js是webpack 的核心

run(callback) {
   //如果正在running，返回报错处理
    if (this.running) return callback(new ConcurrentCompilationError());
    
    //running调用finalCallback 
    const finalCallback = (err, stats) => {
        this.running = false;

        if (callback !== undefined) return callback(err, stats);
    };
    //记录初始化running时间
    const startTime = Date.now();
    //设置running标志，防止多次running
    this.running = true;
    
    //正在编译
    const onCompiled = (err, compilation) => {
        //如果报错，编译结束
        if (err) return finalCallback(err);

        //如果没有编译完成
        if (this.hooks.shouldEmit.call(compilation) === false) {
             // Stats模块有1400行，
             // compiler.js是webpack 的核心，new Stats(compilation)是compiler.js的核心
            const stats = new Stats(compilation);
             //    stats对象挂载startTime，endTime 
            stats.startTime = startTime;
            stats.endTime = Date.now();
            // 异步调用完成事件流，running结束
            this.hooks.done.callAsync(stats, err => {
                if (err) return finalCallback(err);
                return finalCallback(null, stats);
            });
            return;
        }
        // 调用emitAsset方法，emitAsset主要负责写入文件输出文件，不影响我们先看编译
        this.emitAssets(compilation, err => {
            // 类似同上, 如果报错，编译结束
            if (err) return finalCallback(err);
            // 如果需要额外的编译，上次的没编译完成吗😰
            if (compilation.hooks.needAdditionalPass.call()) {
                compilation.needAdditionalPass = true;
                //再来一遍new Stats
                const stats = new Stats(compilation);
                stats.startTime = startTime;
                stats.endTime = Date.now(); 
                //继续异步调用时间流
                this.hooks.done.callAsync(stats, err => {
                    if (err) return finalCallback(err);
                    //  这次多了一个时间流,调用额外编译，告知编译终于编完了
                    this.hooks.additionalPass.callAsync(err => {
                        if (err) return finalCallback(err);
                        //调用compile，把onCompiled的返回值传入compile函数，onCompiled的返回值也就是new Stats的对象
                        this.compile(onCompiled);
                    });
                });
                return;
            }
            // 如果都不走上面的分支，即编译完成，不需要额外的编译
            // 调用emitRecords方法，主要用来记录输出的
            this.emitRecords(err => {
                if (err) return finalCallback(err);
                // 同样new Stats
                const stats = new Stats(compilation);
                stats.startTime = startTime;
                stats.endTime = Date.now();
                // 异步调用完成事件
                this.hooks.done.callAsync(stats, err => {
                    if (err) return finalCallback(err);
                    return finalCallback(null, stats);
                });
            });
            //最终总结，无论走那个分支都是 new Stats(compilation) 返回stats的回调函数,按照目前的流程走的是最后一个分支，调用 this.emitRecords
        });
    };
    
    // 调用beforeRun钩子
    this.hooks.beforeRun.callAsync(this, err => {
        if (err) return finalCallback(err);
        // 调用run钩子
        this.hooks.run.callAsync(this, err => {
            if (err) return finalCallback(err);
            //读文件记录
            this.readRecords(err => {
                if (err) return finalCallback(err);
                //把onCompiled函数传入，调用compile
                this.compile(onCompiled);
            });
        });
    });
}

new Stats(compilation)是compiler.js的核心

compilation和Stats分别对应两个模块

compilation.js 2500行，Stats.js 1400行

接下来我们看一下compile函数

newCompilationParams() {
        const params = {
            // 普通模块工厂
            normalModuleFactory: this.createNormalModuleFactory(),
            // 上下文模块工厂
            contextModuleFactory: this.createContextModuleFactory(),
            // 编译依赖
            compilationDependencies: new Set()
        };
        return params;
    }


compile(callback) {
    // params值如下
    const params = this.newCompilationParams();
    // 异步调用beforeCompile钩子
    this.hooks.beforeCompile.callAsync(params, err => {
        if (err) return callback(err);
        // 调用compile钩子
        this.hooks.compile.call(params);
        // 终于出现了compilation，之前一直没有讲了compilation是什么，newCompilation我们看如下函数
        const compilation = this.newCompilation(params);

        this.hooks.make.callAsync(compilation, err => {
            if (err) return callback(err);

            compilation.finish();

            compilation.seal(err => {
                if (err) return callback(err);
                // 异步调用afterCompile，返回回调函数
                this.hooks.afterCompile.callAsync(compilation, err => {
                    if (err) return callback(err);

                    return callback(null, compilation);
                });
            });
        });
    });
}

newCompilation(params) {
   // compilation 是 this.createCompilation()，继续往下
    const compilation = this.createCompilation();
    //给compilation对象挂载属性
    compilation.fileTimestamps = this.fileTimestamps;
    compilation.contextTimestamps = this.contextTimestamps;
    compilation.name = this.name;
    compilation.records = this.records;
    compilation.compilationDependencies = params.compilationDependencies;
    //告知钩子调用完毕
    this.hooks.thisCompilation.call(compilation, params);
    this.hooks.compilation.call(compilation, params);
    return compilation;
}

createCompilation() {
   // 原来compilation 是 newCompilation而来，Compilation一共2500行，堪称整个compiler.js的核心
    return new Compilation(this);
}

params如下

{ normalModuleFactory:
   NormalModuleFactory {
     _pluginCompat:
      SyncBailHook {
      // key是tapable 方法名
        _args: [Array],
        taps: [Array],
        interceptors: [],
        call: [Function: lazyCompileHook],
        promise: [Function: lazyCompileHook],
        callAsync: [Function: lazyCompileHook],
        _x: undefined },
     hooks:
      { resolver: [SyncWaterfallHook],
        factory: [SyncWaterfallHook],
        beforeResolve: [AsyncSeriesWaterfallHook],
        afterResolve: [AsyncSeriesWaterfallHook],
        createModule: [SyncBailHook],
        module: [SyncWaterfallHook],
        createParser: [HookMap],
        parser: [HookMap],
        createGenerator: [HookMap],
        generator: [HookMap] },
     resolverFactory:
      ResolverFactory {
        _pluginCompat: [SyncBailHook],
        hooks: [Object],
        cache1: [WeakMap],
        cache2: Map {} },
     ruleSet: RuleSet { references: {}, rules: [Array] },
     cachePredicate: [Function: bound Boolean],
     //文件路径
     context: '/Users/orion/Desktop/react-beauty-highcharts',
     parserCache: {},
     generatorCache: {} },
  contextModuleFactory:
   ContextModuleFactory {
     _pluginCompat:
      SyncBailHook {
        _args: [Array],
        taps: [Array],
        interceptors: [],
        call: [Function: lazyCompileHook],
        promise: [Function: lazyCompileHook],
        callAsync: [Function: lazyCompileHook],
        _x: undefined },
     hooks:
      { beforeResolve: [AsyncSeriesWaterfallHook],
        afterResolve: [AsyncSeriesWaterfallHook],
        contextModuleFiles: [SyncWaterfallHook],
        alternatives: [AsyncSeriesWaterfallHook] },
     resolverFactory:
      ResolverFactory {
        _pluginCompat: [SyncBailHook],
        hooks: [Object],
        cache1: [WeakMap],
        cache2: Map {} } },
  compilationDependencies: Set {} }

终极总结

• Compiler构造函数 ->
• run方法 ->
• this.compile(onCompiled) ->
• this.compile()执行有了compilation ->
• onCompiled执行 const stats = new Stats(compilation)
• 最后返回 finalCallback(null, stats);

this.compile(onCompiled) 是个高阶函数，可以简单的理解为参数是函数，并且返回一个函数

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