摘要：小尾巴最終返回了屬性掛載把引入的函數(shù)模塊全部暴露出來下面暴露了一些插件再通俗一點的解釋比如當(dāng)你你能調(diào)用文件下的方法這個和上面的不同在于上面的是掛在函數(shù)對象上的正題要想理解必須要理解再寫一遍地址我們先簡單的理解它為一個通過注冊插件是插件的事

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;
}

最終返回了compiler

  
exports.version = version;

// ...屬性掛載,把引入的函數(shù)模塊全部暴露出來
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")}
)

再通俗一點的解釋：

比如當(dāng)你api.AutomaticPrefetchPlugin你能
調(diào)用AutomaticPrefetchPlugin文件下的方法

這個和上面的不同在于上面的是掛在webpack函數(shù)對象上的

要想理解Compiler.js
必須要理解tapable
再寫一遍 git地址

我們先簡單的理解它為一個通過tap 注冊插件
call是run插件的事件流，里面還有一些異步的操作

Compiler整理如下

class Compiler extends Tapable {
    constructor(context) {
        super();
        this.hooks = {
            //羅列一些出現(xiàn)頻率比較高的
            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) {
        //... 
    }
    // 清除輸入文件系統(tǒng)
    purgeInputFileSystem() {
        if (this.inputFileSystem && this.inputFileSystem.purge) {
            this.inputFileSystem.purge();
        }
    }
    emitAssets(compilation, callback) {
        //...
    }
    createChildCompiler(
        compilation,
        compilerName,
        compilerIndex,
        outputOptions,
        plugins
    ) {
        //...
    
        
    }
    //...
    compile(callback){
        //...
    }    
}

和tapable用法一個模子里刻出來的，我們仔細(xì)的研究run函數(shù)

compiler.js是webpack 的核心

run(callback) {
   //如果正在running，返回報錯處理
    if (this.running) return callback(new ConcurrentCompilationError());
    
    //running調(diào)用finalCallback 
    const finalCallback = (err, stats) => {
        this.running = false;

        if (callback !== undefined) return callback(err, stats);
    };
    //記錄初始化running時間
    const startTime = Date.now();
    //設(shè)置running標(biāo)志，防止多次running
    this.running = true;
    
    //正在編譯
    const onCompiled = (err, compilation) => {
        //如果報錯，編譯結(jié)束
        if (err) return finalCallback(err);

        //如果沒有編譯完成
        if (this.hooks.shouldEmit.call(compilation) === false) {
             // Stats模塊有1400行，
             // compiler.js是webpack 的核心，new Stats(compilation)是compiler.js的核心
            const stats = new Stats(compilation);
             //    stats對象掛載startTime，endTime 
            stats.startTime = startTime;
            stats.endTime = Date.now();
            // 異步調(diào)用完成事件流，running結(jié)束
            this.hooks.done.callAsync(stats, err => {
                if (err) return finalCallback(err);
                return finalCallback(null, stats);
            });
            return;
        }
        // 調(diào)用emitAsset方法，emitAsset主要負(fù)責(zé)寫入文件輸出文件，不影響我們先看編譯
        this.emitAssets(compilation, err => {
            // 類似同上, 如果報錯，編譯結(jié)束
            if (err) return finalCallback(err);
            // 如果需要額外的編譯，上次的沒編譯完成嗎