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Node.js CommonJS Module 实现示例
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| const path = require("path"); | |
| const vm = require("vm"); | |
| const fs = require("fs"); | |
| const cache = Object.create(null); | |
| const extensions = Object.create(null, { | |
| ".js": { | |
| value: (module, filename) => { | |
| const content = fs.readFileSync(filename, "utf-8"); | |
| module._compile(content, filename); | |
| }, | |
| }, | |
| ".json": { | |
| value: (module, filename) => { | |
| const content = fs.readFileSync(filename, "utf-8"); | |
| module.exports = JSON.parse(content); | |
| }, | |
| }, | |
| }); | |
| const wrap = (code) => `(function (exports, require, module, __filename, __dirname) { ${code} });`; | |
| const resolveFilename = (request) => { | |
| const filename = path.resolve(request); | |
| const extname = path.extname(request); | |
| if (!extname) { | |
| for (const ext of Object.keys(extensions)) { | |
| const filepath = `${filename}${ext}`; | |
| if (fs.existsSync(filepath)) { | |
| return filepath; | |
| } | |
| } | |
| } | |
| return filename; | |
| }; | |
| const load = (request) => { | |
| const filename = resolveFilename(request); | |
| // 命中缓存就直接返回，不再加载模块 | |
| const cachedModule = cache[filename]; | |
| if (cachedModule) { | |
| return cachedModule.exports; | |
| } | |
| const module = new Module(filename); | |
| cache[filename] = module; // 缓存模块 | |
| module.load(); | |
| return module.exports; | |
| }; | |
| class Module { | |
| constructor(id = "") { | |
| this.id = id; | |
| this.path = path.dirname(id); | |
| this.exports = {}; | |
| this.filename = null; | |
| this.loaded = false; | |
| } | |
| static _cache = cache; | |
| static _extensions = extensions; | |
| static wrap = wrap; | |
| static _resolveFilename = resolveFilename; | |
| static _load = load; | |
| require(id) { | |
| return load(id); | |
| } | |
| load() { | |
| this.filename = filename; | |
| const extname = path.extname(this.filename); | |
| extensions[extname](this, this.filename); | |
| this.loaded = true; | |
| } | |
| _compile(content) { | |
| const wrapped = wrap(content); | |
| // 在当前 global 对象的上下文中编译并执行 code，最后返回结果 | |
| // 返回值是一个可调用的函数 | |
| const compiled = vm.runInThisContext(wrapped, { filename: this.filename }); | |
| const dirname = path.dirname(this.filename); | |
| // 调用并传入四个参数 | |
| Reflect.apply(compiled, this.exports, [ | |
| this.exports, | |
| this.require, | |
| this, | |
| this.filename, | |
| dirname, | |
| ]); | |
| } | |
| } | |
| exports = module.exports = Module; | |
| // 用法 | |
| // Module._load("xxx.js"); |
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