模拟webpack 实现本身的打包工具

时间  2020-05-07
标签 模拟 webpack 实现 本身 打包 工具 繁體版
原文   原文链接

本框架模拟webpack打包工具javascript

详细代码个步骤请看git地址：https://github.com/jiangzhenfei/easy-webpackcss

建立package.json

{ "name": "simple-webpack", "version": "1.0.0", "description": "", "main": "index.js", "directories": { "lib": "lib" }, "scripts": { "mywebpack": "node ./bin/mwebpack.js" }, "author": "", "license": "ISC", "dependencies": { } }

 

建立/bin/mwebpack.js

#! /usr/bin/env node        /*标注文件的运行环境*/ const path = require('path'); const fs = require('fs'); //当前工做目录
const root = process.cwd(); //引入Compiler
const Compiler = require('../lib/Compiler'); //配置文件和 Shell 语句中读取与合并参数,这里简化逻辑，没有处理shell部分
let options = require(path.resolve(__dirname,'../webpack.config.js')); //初始化compiler对象加载全部配置的插件
let compiler = new Compiler(options); // 执行对象的 run 方法开始执行编译
compiler.run();

 

初始化Compiler

在当前目录下建立/lib/Compiler.jsjava

const path = require('path'); const fs = require('fs'); class Compiler { constructor(options){ this.options = options; } run(){ console.log('---------start---------') } } module.exports = Compiler

 

完善run方法

const path = require('path');
const fs = require('fs');
class Compiler {
    constructor(options){
        this.options = options;
    }
    run(){
        let that = this;
        let {entry} = this.options; // 获取webpck.config.js中的entry
        this.root = process.cwd();      
        this.entryId = null;        //记录入口的id，这里采用单入口简化
        this.modules = {};          //缓存入口的依赖，这里采用单入口简化
        
        // 找出该模块依赖的模块
        //再递归本步骤直到全部入口依赖的文件都通过了本步骤的处理
        this.buildModule(path.resolve(this.root, entry), true);
        
        // 输出资源
        this.emitFile();
    }
}
module.exports = Compiler

　　

编写buildModule

编译模块：从入口文件出发，调用全部配置的Loader对模块进行翻译，再找出该模块依赖的模块，再递归本步骤直到全部入口依赖的文件都通过了本步骤的处理 完成模块编译：在通过第4步使用Loader翻译完全部模块后，获得了每一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，再把每一个 Chunk 转换成一个单独的文件加入到输出列表，这步是能够修改输出内容的最后机会node

const path = require('path'); const fs = require('fs'); class Compiler { constructor(options){ this.options = options; } run(){ let that = this; let {entry} = this.options; this.root = process.cwd(); this.entryId = null; this.modules = {}; this.buildModule(path.resolve(this.root, entry), true); this.emitFile(); } getSource(modulePath) { let source = fs.readFileSync(modulePath, 'utf8'); //TODO：loader的处理逻辑写在这里，后面会提到
        
        return source; } buildModule(modulePath,isEntry){ let that = this; let source = this.getSource(modulePath);//获取源代码
        
        //生成相对于工做根目录的模块ID，相对路径exp：'./sec/index'
        let moduleId = './' + path.relative(this.root, modulePath); //若是是入口的话把id赋给compiler对象的入口
        if (isEntry) { this.entryId = moduleId; } //获取AST的编译结果，获取依赖的模块，而且将代码进行转换
        let { dependencies, sourcecode } = this.parse(source, path.dirname(moduleId)); this.modules[moduleId] = sourcecode; //递归解析依赖的模块
        dependencies.forEach(dependency => that.buildModule(path.join(that.root, dependency))); } emitFile(){ } } module.exports = Compiler

 

编写parse函数

编译模块：从入口文件出发，调用全部配置的Loader对模块进行翻译，再找出该模块依赖的模块，再递归本步骤直到全部入口依赖的文件都通过了本步骤的处理 代码转换成AST，webpack中使用的Acorn，这里使用babel-types，babel-traverse，babel-generator替代： babylon把源码转成AST babel-types生成节点或者判断节点类型 babel-traverse遍历AST，捕获指定的节点 babel-generator将AST从新生成代码webpack

npm install babylon babel-types babel-generator babel-traverse

查看原生webpack生成的bundle.js，须要将require换成__webpack_require__，而且将路径修改成相对于根目录的相对路径git

把js文件内容解析ast，而且分析require依赖es6

const path = require('path'); const fs = require('fs'); const babylon = require('babylon'); const t = require('babel-types'); //采用es6的写法，因此要在后面添加.default
const traverse = require('babel-traverse').default; const generator = require('babel-generator').default; class Compiler { constructor(options){ this.options = options; } run(){ let that = this; let {entry} = this.options; this.root = process.cwd(); this.entryId = null; this.modules = {}; this.buildModule(path.resolve(this.root, entry), true); this.emitFile(); } getSource(modulePath) { let source = fs.readFileSync(modulePath, 'utf8'); //TODO：loader的处理逻辑写在这里，后面会提到
        return source; } buildModule(modulePath,isEntry){ let that = this; let source = this.getSource(modulePath); let moduleId = './' + path.relative(this.root, modulePath); if (isEntry) { this.entryId = moduleId; } let { dependencies, sourcecode } = this.parse(source, path.dirname(moduleId)); this.modules[moduleId] = sourcecode; dependencies.forEach(dependency => that.buildModule(path.join(that.root, dependency))); } parse(source, parentPath) { let that = this; let ast = babylon.parse(source);    //源码转语法树
        let dependencies = [];      //存储依赖的模块路径
        //遍历AST找到对应的节点进行修改
 traverse(ast, { CallExpression(p) {//p当前路径
                if (p.node.callee.name == 'require') { let node = p.node; //修改方法名
                    node.callee.name = '__webpack_require__'; // 获得模块名exp:'./a'
                    let moduleName = node.arguments[0].value; //若是须要的话，添加.js后缀 
                    moduleName += (moduleName.lastIndexOf('.') > 0 ? '' : '.js'); //获得依赖模块的id，exp:'./src/a'
                    let moduleId = './' + path.relative(that.root, path.join(parentPath, moduleName)); //相对于根目录的相对路径
                    node.arguments = [t.stringLiteral(moduleId)]; //把模块id放置到当前模块的依赖列表里
 dependencies.push(moduleId); } } }); //将修改的AST从新生成代码
        let sourcecode = generator(ast).code; return { sourcecode, dependencies }; } emitFile(){ } } module.exports = Compiler

 

编写emitFile函数

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，再把每一个 Chunk转换成一个单独的文件加入到输出列表，这步是能够修改输出内容的最后机会 每次编译打包后，都会发现webpack打包后的结果很大部分都是同样的，能够抽离出一个模板用来构建每次打包的结果： 建立entry.ejs文件github

// MainTemplate这里采用ejs模板简化
(function(modules) {
    var installedModules = {}; 
    function __webpack_require__(moduleId) {
        if (installedModules[moduleId]) {
            return installedModules[moduleId].exports;
        }
        var module = (installedModules[moduleId] = {
            i: moduleId,
            l: false,
            exports: {}
        });
        modules[moduleId].call(
            module.exports,
            module,
            module.exports,
            __webpack_require__
        );
        module.l = true;
        return module.exports;
    }
        return __webpack_require__((__webpack_require__.s = "<%-entryId%>"));
})({
    <%for (let moduleId in modules) {let source = modules[moduleId];%>
        "<%-moduleId%>":(function(module,exports,__webpack_require__){eval(`<%-source%>`);}),
    <% }%>
});
完善emitFile函数
const path = require('path'); const fs = require('fs'); const babylon = require('babylon'); const t = require('babel-types'); const traverse = require('babel-traverse').default; const generator = require('babel-generator').default; const ejs = require('ejs');     //引入ejs
class Compiler { constructor(options){ this.options = options; } run(){ let that = this; let {entry} = this.options; this.root = process.cwd(); this.entryId = null; this.modules = {}; this.buildModule(path.resolve(this.root, entry), true); this.emitFile(); } getSource(modulePath) { let source = fs.readFileSync(modulePath, 'utf8'); //TODO：loader的处理逻辑写在这里，后面会提到
        return source; } buildModule(modulePath,isEntry){ let that = this; let source = this.getSource(modulePath); let moduleId = './' + path.relative(this.root, modulePath); if (isEntry) { this.entryId = moduleId; } let { dependencies, sourcecode } = this.parse(source, path.dirname(moduleId)); this.modules[moduleId] = sourcecode; dependencies.forEach(dependency => that.buildModule(path.join(that.root, dependency))); } parse(source, parentPath) { let that = this; let ast = babylon.parse(source); let dependencies = []; traverse(ast, { CallExpression(p) { if (p.node.callee.name == 'require') { let node = p.node; node.callee.name = '__webpack_require__'; let moduleName = node.arguments[0].value; moduleName += (moduleName.lastIndexOf('.') > 0 ? '' : '.js'); let moduleId = './' + path.relative(that.root, path.join(parentPath, moduleName)); node.arguments = [t.stringLiteral(moduleId)]; dependencies.push(moduleId); } } }); let sourcecode = generator(ast).code; return { sourcecode, dependencies }; } emitFile(){ // 读取模板文件
        let entryTemplate = fs.readFileSync(path.join(__dirname, 'entry.ejs'), 'utf8'); // 获取渲染的数据
        let { entryId, modules } = this; // 将数据渲染到模板上
        let source = ejs.compile(entryTemplate)({ entryId, modules }); //找到目标路径
        let target = path.join(this.options.output.path, this.options.output.filename); //将渲染后的模板目标文件
 fs.writeFileSync(target, source); } } module.exports = Compiler

 

实现loader功能

上面的webpack已经具有打包js的功能了，可是还不能打包css等文件，原生的webpack是经过各类loader来打包css等其余文件的，因此再getSource时调用loader，将其余文件处理成js，而后进行后面的操做web

新建less-loader模拟less-loader插件
var less = require('less'); module.exports = function (source) { let css; less.render(source, (err, output) => { css = output.css; }); return css.replace(/\n/g, '\\n', 'g'); }

 

新建style-loader模拟style-loader插件
//style-loader的功能就是将加载的css文件放在style标签中插入到页面
module.exports = function (source) { let str = ` let style = document.createElement('style'); style.innerHTML = ${JSON.stringify(source)}; document.head.appendChild(style); `; return str; }

 

完善构建过程shell

const path = require('path'); const fs = require('fs'); const babylon = require('babylon'); const t = require('babel-types'); const traverse = require('babel-traverse').default; const generator = require('babel-generator').default; const ejs = require('ejs');     //引入ejs
class Compiler { constructor(options){ this.options = options; } run(){ let that = this; let {entry} = this.options; this.root = process.cwd(); this.entryId = null; this.modules = {}; this.buildModule(path.resolve(this.root, entry), true); this.emitFile(); } getSource(modulePath) { let source = fs.readFileSync(modulePath, 'utf8'); //获取webpack.config.js中的rules
        let rules = that.options.module.rules; //遍历rules调用loader
        for (let i = 0; i < rules.length; i++) { let rule = rules[i]; // 用rule的test中正则匹配文件的类型是否须要使用laoder
            if (rule.test.test(modulePath)) { //获取rule中的loaders，例如['style-laoder','css-loader']
                let loaders = rule.use; let length = loaders.length;    //loader的数量 
                let loaderIndex = length - 1;   // 往右向左执行
                
                // loader遍历器
                function iterateLoader() { let loaderName = loaders[loaderIndex--]; //loader只是一个包名，须要用require引入
                    let loader = require(path.join(that.root, loaderName)); //使用loader，能够看出loader的本质是一个函数
                    source = loader(source); if (loaderIndex >= 0) { iterateLoader(); } } //遍历执行loader
 iterateLoader(); } } return source; } buildModule(modulePath,isEntry){ let that = this; let source = this.getSource(modulePath); let moduleId = './' + path.relative(this.root, modulePath); if (isEntry) { this.entryId = moduleId; } let { dependencies, sourcecode } = this.parse(source, path.dirname(moduleId)); this.modules[moduleId] = sourcecode; dependencies.forEach(dependency => that.buildModule(path.join(that.root, dependency))); } parse(source, parentPath) { let that = this; let ast = babylon.parse(source); let dependencies = []; traverse(ast, { CallExpression(p) { if (p.node.callee.name == 'require') { let node = p.node; node.callee.name = '__webpack_require__'; let moduleName = node.arguments[0].value; moduleName += (moduleName.lastIndexOf('.') > 0 ? '' : '.js'); let moduleId = './' + path.relative(that.root, path.join(parentPath, moduleName)); node.arguments = [t.stringLiteral(moduleId)]; dependencies.push(moduleId); } } }); let sourcecode = generator(ast).code; return { sourcecode, dependencies }; } emitFile(){ let entryTemplate = fs.readFileSync(path.join(__dirname, 'entry.ejs'), 'utf8'); let { entryId, modules } = this; let source = ejs.compile(entryTemplate)({ entryId, modules }); let target = path.join(this.options.output.path, this.options.output.filename); fs.writeFileSync(target, source); } } module.exports = Compiler

 

建立/src/index.less

@color: #000; body{ color: @color;
}

 

修改/src/index.js

require('index.less')

 

修改webpack.config.js

module.exports = { entry: './src/index.js', output: { path: './', filename: 'bundle.js' }, module: { rules: [ { test: /\.less$/, use: ['style-loader', 'less-loader'] } ] }, plugins: [ ] }

 

实现plugin功能

原生webpack支持不少种插件，在webpack编译的过程当中的各个阶段使用，常见的一些钩子：

entryOption 读取配置文件 afterPlugins 加载全部的插件 run 开始执行编译流程 compile 开始编译 afterCompile 编译完成 emit 写入文件 done 完成总体流程 修改bin/mwebpack.js 注册规则阶段的钩子，供用户订阅来执行插件。

const path = require('path'); const fs = require('fs'); const babylon = require('babylon'); const t = require('babel-types'); //采用es6的写法，因此要在后面添加.default
const traverse = require('babel-traverse').default; const generator = require('babel-generator').default; const ejs = require('ejs');     //引入ejs //使用tapable来建立发布者，利用call等来触发
const { SyncHook } = require('tapable'); class Compiler { constructor(options){ this.options = options; this.hooks = { entryOption: new SyncHook(), afterPlugins: new SyncHook(), run: new SyncHook(), beforeCompile: new SyncHook(), afterCompile: new SyncHook(), emit: new SyncHook(), afterEmit: new SyncHook(), done: new SyncHook(), } } run(){ let compiler = this; compiler.hooks.run.call(); //触发run
 let {entry} = this.options; this.root = process.cwd(); this.entryId = null; this.modules = {}; compiler.hooks.beforeCompile.call(); //触发beforeCompile

        this.buildModule(path.resolve(this.root, entry), true); compiler.hooks.afterCompile.call(); //afterCompile

        this.hooks.emit.call();                 //触发emit
        this.emitFile(); compiler.hooks.afterEmit.call(); //触发afterEmit
        compiler.hooks.done.call();             //触发done
 } getSource(modulePath) { let source = fs.readFileSync(modulePath, 'utf8'); let that = this; //获取webpack.config.js中的rules
        let rules = that.options.module.rules; //遍历rules调用loader
        for (let i = 0; i < rules.length; i++) { let rule = rules[i]; // 用rule的test中正则匹配文件的类型是否须要使用laoder
            if (rule.test.test(modulePath)) { //获取rule中的loaders，例如['style-laoder','css-loader']
                let loaders = rule.use; let length = loaders.length;    //loader的数量 
                let loaderIndex = length - 1;   // 往右向左执行
                
                // loader遍历器
                function iterateLoader() { let loaderName = loaders[loaderIndex--]; //loader只是一个包名，须要用require引入
                    let loader = require(path.join(that.root, loaderName)); //使用loader，能够看出loader的本质是一个函数
                    source = loader(source); if (loaderIndex >= 0) { iterateLoader(); } } //遍历执行loader
 iterateLoader(); break; } } return source; } buildModule(modulePath,isEntry){ let that = this; let source = this.getSource(modulePath); let moduleId = './' + path.relative(this.root, modulePath); if (isEntry) { this.entryId = moduleId; } let { dependencies, sourcecode } = this.parse(source, path.dirname(moduleId)); this.modules[moduleId] = sourcecode; dependencies.forEach(dependency => that.buildModule(path.join(that.root, dependency))); } parse(source, parentPath) { let that = this; let ast = babylon.parse(source);    //源码转语法树
        let dependencies = [];      //存储依赖的模块路径
        //遍历AST找到对应的节点进行修改
 traverse(ast, { CallExpression(p) {//p当前路径
                if (p.node.callee.name == 'require') { let node = p.node; //修改方法名
                    node.callee.name = '__webpack_require__'; // 获得模块名exp:'./a'
                    let moduleName = node.arguments[0].value; //若是须要的话，添加.js后缀 
                    moduleName += (moduleName.lastIndexOf('.') > 0 ? '' : '.js'); //获得依赖模块的id，exp:'./src/a'
                    let moduleId = './' + path.relative(that.root, path.join(parentPath, moduleName)); //相对于根目录的相对路径
                    node.arguments = [t.stringLiteral(moduleId)]; //把模块id放置到当前模块的依赖列表里
 dependencies.push(moduleId); } } }); //将修改的AST从新生成代码
        let sourcecode = generator(ast).code; return { sourcecode, dependencies }; } emitFile(){ // 读取模板文件
        let entryTemplate = fs.readFileSync(path.join(this.root, 'entry.ejs'), 'utf8'); // 获取渲染的数据
        let { entryId, modules } = this; // 将数据渲染到模板上
        let source = ejs.compile(entryTemplate)({ entryId, modules }); //找到目标路径
        let target = path.join(this.root,this.options.output.path, this.options.output.filename); //将渲染后的模板目标文件
 fs.writeFileSync(target, source); } } module.exports = Compiler

 

#! /usr/bin/env node        /*标注文件的运行环境*/ const path = require('path'); const fs = require('fs'); //当前工做目录
const root = process.cwd(); //引入Compiler
const Compiler = require('../lib/Compiler');

 

//配置文件和 Shell 语句中读取与合并参数,这里简化逻辑，没有处理shell部分
let options = require(path.resolve(__dirname,'../webpack.config.js')); //初始化compiler对象加载全部配置的插件
let compiler = new Compiler(options); compiler.hooks.entryOption.call(); //触发entryOptions
 let {plugins} = options; plugins.forEach(plugin => { plugin.apply(compiler) }); compiler.hooks.afterPlugins.call(), //触发afterPlugins


// 执行对象的 run 方法开始执行编译
compiler.run();

 

 
const { EntryOptionWebpackPlugin, AfterPlugins, RunPlugin, CompileWebpackPlugin, AfterCompileWebpackPlugin, EmitWebpackPlugin, DoneWebpackPlugin } = require('./plugins') module.exports = { entry: './src/index.js', output: { path: './', filename: 'bundle.js' }, module: { rules: [ { test: /\.less$/, use: ['style-loader', 'less-loader'] } ] }, plugins: [ new EntryOptionWebpackPlugin(), new AfterPlugins(), new RunPlugin(), new CompileWebpackPlugin(), new AfterCompileWebpackPlugin(), new EmitWebpackPlugin(), new DoneWebpackPlugin() ] }

 

执行npm run mywebpack 能够看到

##结语 webpack的主要工做： 合并option，获取plugin注册插件 run得到入口文件，用loader对入口文件进行处理， 将其转化为AST进行代码修改，递归分析其依赖的模块 根据入口文件的依赖项，将其渲染到对应的模板文件，而后写到出口文件中

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