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(lái)下面暴露了一些插件再通俗一點(diǎn)的解釋比如當(dāng)你你能調(diào)用文件下的方法這個(gè)和上面的不同在于上面的是掛在函數(shù)對(duì)象上的正題要想理解必須要理解再寫一遍地址我們先簡(jiǎn)單的理解它為一個(gè)通過(guò)注冊(cè)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(lái)
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(diǎn)的解釋：

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

這個(gè)和上面的不同在于上面的是掛在webpack函數(shù)對(duì)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(jiǎn)單的理解它為一個(gè)通過(guò)tap 注冊(cè)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(gè)模子里刻出來(lái)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(bào)錯(cuò)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(shí)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(bào)錯(cuò)，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(duì)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(bào)錯(cuò)，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