Node.js require 模块加载原理 All In One

合集 - Node.js(100)

1.Adafruit & CircuitPython & Node.js All In One2023-05-182.Node.js os module All In One2023-05-143.Node.js & Raspberry Pi & WS2812B RGB LEDs strip All In One2023-05-124.Node.js Buffer.from All In One2023-04-265.Node.js Event Loop & V8 engine & libuv All In One2023-04-236.Node.js & npm package.json exports field All In One2023-03-217.Node.js cli tools auto install npm packages All In One2023-03-168.Node.js 微服务 All In One2023-03-159.如何定位和分析 Node.js 项目中的内存泄漏问题 All In One2023-03-1310.Node.js process.nextTick All In One2023-02-2811.Web API setImmediate & Node.js setImmediate All In One2023-02-2812.如何使用 Node.js 和 OpenAI API 快速开发一个私有的 ChatGPT 智能聊天机器人程序 All In One2023-02-0813.how to config `node.js` version in vercel All In One2022-12-0214.Node.js & file system & async await & forEach bug All In One2022-11-2915.Microsoft & Node.js All In One2022-11-2716.Node.js fs API docs All In One2022-11-1217.macOS brew uninstall node.js All In One2022-11-1118.nvm & grep filter out only Node.js Latest LTS versions All In One2022-11-0219.Node.js ORM All In One2022-10-1320.How to exit Node.js REPL environment All In One2022-09-2221.Node.js 面试题 All In One2022-09-2122.How to custom your own Node.js Docker Image All In One2022-07-2623.Node.js 中 CommonJS 模块 exports 与 module.exports 实现原理剖析 All In One2022-04-2624.change nvm default Node.js version All In One2022-04-1925.Node.js path All In One2022-04-1726.如何使用 Node.js 服务器控制浏览器下载文件还是预览文件 All In One2022-04-1727.Node.js server render Blob file All In One2022-04-0928.how to exit terminal from a Node.js program All In One2022-04-0629.Node.js CommonJS __dirname ../ relative path bug All In One2022-04-0430.Node.js import ESM module error All In One2022-04-0431.TypeScript & Node.js crawler All In One2022-04-0132.Node.js process All In One2022-03-1333.autoprefixer: ignore next not work bug All In One2022-01-2634.如何判断当前 js 代码是运行在浏览器还是node环境中 All In One2022-01-1635.Node.js project auto open localhost with ip address All In One2021-12-2236.Node.js & TypeScript error All In One2021-11-1437.Node.js & child_process All In One2021-10-2038.cross-env & shelljs & set custom node.js env All In One2021-10-1539.nvm set system node version All In One2021-06-1740.Node.js 设置内存大小 All In One2021-06-1541.Node.js & ES Modules & TypeScript All In One2021-05-2142.Node.js & TS & VSCode error All In One2021-05-2143.Node.js & Express server support CORS2021-04-3044.Node.js in action All In One2021-04-1445.Node.js & Express.js Server get binary data All In One2021-04-0846.node.js & webpack proxy bug2021-04-0747.Node.js 实战（第2版）All In One2021-04-0648.node.js ECONNRESET error2021-03-2949.node.js cli downloader2021-01-2350.Node.js 文件上传 cli tools2021-01-1751.Node.js 实战 & 最佳 Express 项目架构2021-01-1152.cnblogs blogs backup & node.js crawler2021-01-0753.Node.js 返回 JSON 数据2020-12-2154.node.js 怎么扩大默认的分配的最大运行内存2020-12-1555.Node.js fs API _dirname & _filename & path All In One2020-11-1656.Node.js Backend Developer2020-10-25

57.Node.js require 模块加载原理 All In One2020-10-05

58.node.js module.exports & exports & module.export all in one2020-10-0559.Nest.js tutorials All In One2020-09-1360.PM2 & nodemon & Node.js Deamon All In One2020-09-0661.node.js 中间件2020-09-0262.node --experimental-modules & node.js ES Modules2020-08-3163.Express All In One2020-08-3064.Node.js & ES Modules & Jest2020-08-2965.how to config custom process.env in Node.js All In One2020-08-1466.一个最简单 node.js 命令行工具2020-07-1767.Node.js delete directory & file system All In One2020-07-0968.Node.js Learning Paths All In One2020-07-0869.Deno 1.0 & Node.js All In One2020-05-1770.Node.js & ORM & ODM All In One2020-05-1071.Node.js & BFF & FaaS2020-05-0572.Node.js 如何处理一个很大的文件 All In One2020-04-2773.Node.js RESTful API & EJS template engine All In One2020-04-2174.Node.js & ES modules & .mjs2020-02-2375.Node.js & 页面截图 & 生成画报 All In One2020-02-1976.Node.js & LTS2020-02-1877.Node.js Debugger All In One2020-02-1078.VSCode & Node.js & debugger & inspector2020-02-0879.玩转 Node.js & React 系列教程：graphql 教程2019-10-1980.Node.js & module.exports & exports All In One2019-09-0381.Node.js & process.env & OS Platform checker2019-05-3082.How to write a Node.js cli tools step by step tutorials All In One2019-05-1383.node.js & read argv2019-05-1384.Node.js & create file All In One2019-05-1385.Docker & Node.js2019-05-1086.NAIO & Node.js All In One2019-05-0887.node.js & fs & file read & file write All In One2019-05-0788.node.js & Unbuntu Linux & nvm & npm2019-05-0789.Node.js & SSR2019-02-2590.nodejs & docker2018-11-1291.Node.js & Koa.js All In One2018-10-1092.mongodb & vue & node.js2018-10-1093.Node.js & module system2018-08-1794.Node.js Spider2017-06-0495.How to Install Multiple Versions of Node.js on the same Server(PC) All In One2016-09-1896.how to updating Node.js and npm2016-09-1897.Node.js : npm-install 教程2016-08-1398.node.js && npm commands2016-07-0199.node.js <=> Command Line Options2016-06-28100.有关 Node.js, npm 和 modules 安装及使用方法的个人总结！All In One2015-09-18

收起

Node.js require 模块加载原理 All In One

require 加载模块，搜索路径

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-10-01
 * @modified
 *
 * @description
 * @difficulty Easy Medium Hard
 * @complexity O(n)
 * @augments
 * @example
 * @link
 * @solutions
 *
 * @best_solutions
 *
 */

const log = console.log;

function Module(id, parent) {
  this.id = id;
  this.path = id;
  // path = (id - filename.js)
  this.paths = [];
  // [paths1, parent path, ..., root path]
  // paths1 = (id - filename.js) + node_modules
  this.exports = {};
  this.parent = parent;
  this.filename = null;
  this.loaded = false;
  this.children = [];
}

// ✅ 在原型上添加只有实例才可以访问的实例方法 require
Module.prototype.require = function(path) {
  // 调用构造函数的静态方法 Module._load
  return Module._load(path, this);
};

// 用模块的绝对路径，那么除了 module.filename
// Node 还提供一个 require.resolve 方法，供外部调用，用于从模块名取到绝对路径
require.resolve = function(request) {
  return Module._resolveFilename(request, self);
};

Module.prototype.load = function(filename) {
  var extension = path.extname(filename) || '.js';
  if (!Module._extensions[extension]) {
    extension = '.js';
  }
  Module._extensions[extension](this, filename);
  this.loaded = true;
};

// 首先，将模块文件读取成字符串;
// 然后剥离 utf8 编码特有的 BOM 文件头，最后编译该模块.
Module._extensions['.js'] = function(module, filename) {
  var content = fs.readFileSync(filename, 'utf8');
  module._compile(stripBOM(content), filename);
};

Module._extensions['.json'] = function(module, filename) {
  var content = fs.readFileSync(filename, 'utf8');
  try {
    module.exports = JSON.parse(stripBOM(content));
  } catch (err) {
    err.message = filename + ': ' + err.message;
    throw err;
  }
};

Module.prototype._compile = function(content, filename) {
  var self = this;
  var args = [self.exports, require, self, filename, dirname];
  return compiledWrapper.apply(self.exports, args);
}

// 👍 上面的代码基本等同于下面的形式
// (function (exports, require, module, __filename, __dirname) {
//   // 模块源码
// });

Module._load = function(request, parent, isMain) {
  // 计算绝对路径
  var filename = Module._resolveFilename(request, parent);
  //  第一步：如果有缓存，取出缓存
  var cachedModule = Module._cache[filename];
  if (cachedModule) {
    return cachedModule.exports;
  }
  // 第二步：是否为内置模块
  if (NativeModule.exists(filename)) {
    return NativeModule.require(filename);
  }
  // 第三步：生成模块实例，存入缓存
  var module = new Module(filename, parent);
  // ✅ 实例化 module
  Module._cache[filename] = module;
  // 第四步：加载模块
  try {
    module.load(filename);
    hadException = false;
  } finally {
    if (hadException) {
      delete Module._cache[filename];
    }
  }
  // 第五步：输出模块的exports属性
  return module.exports;
}

// Module._cache = [];

Module._resolveFilename = function(request, parent) {
  // 第一步：如果是内置模块，不含路径返回
  if (NativeModule.exists(request)) {
    return request;
  }
  // 第二步：确定所有可能的路径
  var resolvedModule = Module._resolveLookupPaths(request, parent);
  var id = resolvedModule[0];
  var paths = resolvedModule[1];
  // 第三步：确定哪一个路径为真
  var filename = Module._findPath(request, paths);
  if (!filename) {
    var err = new Error("Cannot find module '" + request + "'");
    err.code = 'MODULE_NOT_FOUND';
    throw err;
  }
  return filename;
};

Module._resolveLookupPaths = function(request, parent){
  // 列出可能的路径
}

// 确认哪一个路径为真
Module._findPath = function(request, paths) {
  // 列出所有可能的后缀名：.js，.json, .node
  var exists = Object.keys(Module._extensions);
  // 如果是绝对路径，就不再搜索
  if (request.charAt(0) === '/') {
    paths = [''];
  }
  // 是否有后缀的目录斜杠
  var trailingSlash = (request.slice(-1) === '/');
  // 第一步：如果当前路径已在缓存中，就直接返回缓存
  var cacheKey = JSON.stringify({request: request, paths: paths});
  if (Module._pathCache[cacheKey]) {
    return Module._pathCache[cacheKey];
  }
  // 第二步：依次遍历所有路径
  for (var i = 0, PL = paths.length; i < PL; i++) {
    var basePath = path.resolve(paths[i], request);
    var filename;

    if (!trailingSlash) {
      // 第三步：是否存在该模块文件
      filename = tryFile(basePath);
      if (!filename && !trailingSlash) {
        // 第四步：该模块文件加上后缀名，是否存在
        filename = tryExtensions(basePath, exists);
      }
    }
    // 第五步：目录中是否存在 package.json
    if (!filename) {
      filename = tryPackage(basePath, exists);
    }
    if (!filename) {
      // 第六步：是否存在目录名 + index + 后缀名
      filename = tryExtensions(path.resolve(basePath, 'index'), exists);
    }
    // 第七步：将找到的文件路径存入返回缓存，然后返回
    if (filename) {
      Module._pathCache[cacheKey] = filename;
      return filename;
    }
  }
  // 第八步：没有找到文件，返回false
  return false;
};


module.exports = Module;

// 模块的加载实质上
// 注入 exports、require、module 三个全局变量;
// 然后执行模块的源码;
// 最后将模块的 exports 变量的值输出.

exports = module.exports

✅ module.exports 与 exports 指向同一个Object 引用

https://blog.tableflip.io/the-difference-between-module-exports-and-exports

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-10-01
 * @modified
 *
 * @description
 * @difficulty Easy Medium Hard
 * @complexity O(n)
 * @augments
 * @example
 * @link
 * @solutions
 *
 * @best_solutions
 *
 */

const log = console.log;

// ✅ module.exports 与 exports 指向同一个Object 引用

// SyntaxError: Identifier 'module' has already been declared
// module = {
//   exports: {},
//   //others
// };
// // {exports: {…}}

// module.exports;
// // {}

// exports = module.exports;
// // {}

// exports.a = `a`;

// module.exports.a = `aa`;
// module.exports.b = `b`;

// log(`exports =`, exports);
// log(`module.exports =`, module.exports);

/*

exports = { a: 'aa', b: 'b' }
module.exports = { a: 'aa', b: 'b' }

*/

const test = () => {
  const module = {
    exports: {},
    //others
  };
  // {exports: {…}}
  module.exports;
  // {}
  const exports = module.exports;
  // {}
  exports.a = `a`;
  module.exports.a = `aa`;
  module.exports.b = `b`;
  log(`exports =`, exports);
  log(`module.exports =`, module.exports);
}
test();

/*

exports = { a: 'aa', b: 'b' }
module.exports = { a: 'aa', b: 'b' }

*/

node_modules

  paths: [
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
    '/Users/xgqfrms-mbp/Documents/node_modules',
    '/Users/xgqfrms-mbp/node_modules',
    '/Users/node_modules',
    '/node_modules'
  ]

➜  module.exports git:(master) ✗ node test.js
exports = {}
module.exports = [Function: app] { test: 'abc' }
module Module {
  id: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/app.js',
  path: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports',
  exports: [Function: app] { test: 'abc' },
  parent: Module {
    id: '.',
    path: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports',
    exports: {},
    parent: null,
    filename: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/test.js',
    loaded: false,
    children: [ [Circular] ],
    paths: [
      '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/node_modules',
      '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/node_modules',
      '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/node_modules',
      '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/node_modules',
      '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
      '/Users/xgqfrms-mbp/Documents/node_modules',
      '/Users/xgqfrms-mbp/node_modules',
      '/Users/node_modules',
      '/node_modules'
    ]
  },
  filename: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/app.js',
  loaded: false,
  children: [],
  paths: [
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.exports/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
    '/Users/xgqfrms-mbp/Documents/node_modules',
    '/Users/xgqfrms-mbp/node_modules',
    '/Users/node_modules',
    '/node_modules'
  ]
}

app = [Function: app] { test: 'abc' } undefined
args = []
test = abc

path & paths

function Module(id, parent) {
  this.id = id;
  this.path = path;// id - filename.js
  this.paths = [path, parent path, ..., root path];
  this.exports = {};
  this.parent = parent;
  this.filename = null;
  this.loaded = false;
  this.children = [];
}

module.exports = Module;

var module = new Module(filename, parent);

demo

const log = console.log;

// module.js

log('module.id: ', module.id);
log('module.exports: ', module.exports);
log('module.parent: ', module.parent);
log('module.filename: ', module.filename);
log('module.loaded: ', module.loaded);
log('module.children: ', module.children);
log('module.paths: ', module.paths);

log(`\nmodule =`, module);

/*

$ node module.js

module.id:  .
module.exports:  {}
module.parent:  null
module.filename:  /Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.js
module.loaded:  false
module.children:  []
module.paths:  [
  '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/node_modules',
  '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/node_modules',
  '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/node_modules',
  '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
  '/Users/xgqfrms-mbp/Documents/node_modules',
  '/Users/xgqfrms-mbp/node_modules',
  '/Users/node_modules',
  '/node_modules'
]

*/


/*

module = Module {
  id: '.',
  path: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system',
  exports: {},
  parent: null,
  filename: '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/module.js',
  loaded: false,
  children: [],
  paths: [
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/module-system/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/src/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/learn-node.js-by-practice/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
    '/Users/xgqfrms-mbp/Documents/node_modules',
    '/Users/xgqfrms-mbp/node_modules',
    '/Users/node_modules',
    '/node_modules'
  ]
}

*/

CommonJS

https://en.wikipedia.org/wiki/CommonJS

require() function & module.exports (alias, exports)

default exports

module.exports = xxx;

module.exports.xxx = xxx;
module.exports = {
  xxx: xxx,
};

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-10-01
 * @modified
 *
 * @description
 * @difficulty Easy Medium Hard
 * @complexity O(n)
 * @augments
 * @example
 * @link
 * @solutions
 *
 * @best_solutions
 *
 */

const log = console.log;

const app = (datas = [], debug = false) => {
  log(`datas =`, datas)
};

// 👎❌
// exports = app;

// ✅ module export (const { app, } = require(`./app`);)
// exports.app = app;

// 👍✅ default export (const app = require(`./app`);)
module.exports = app;

// ✅
// module.exports.app = app;

// ✅
// module.exports = {
//   app,
// };

module.exports 覆盖 exports

const log = console.log;

log(`exports`, exports);
log(`module`, module);

// TypeError: Cannot set property 'a' of undefined
// module.export.a = 1;
// module.export.b = 2;
// module.export.c = 3;
// module.export.d = 4;

// 自定义属性 umd ✅
module.umd = {
  a: 1,
  b: 2,
  c: 3,
  d: 4,
};
// 自定义属性 export ✅
module.export = {
  a: 1,
  b: 2,
  c: 3,
  d: 4,
};

exports.a = 11;
exports.b = 22;
exports.c = 33;
exports.d = 44;

// module.exports 覆盖 exports
module.exports = { c: 333 };
module.exports.d = 444;

log(`\nexports`, exports);
log(`module`, module);


/*


exports { a: 11, b: 22, c: 33, d: 44 }
module Module {
  id: '.',
  path: '/Users/xgqfrms-mbp/Documents/GitHub/umd-npm-package/src',
  exports: { c: 333, d: 444 },
  parent: null,
  filename: '/Users/xgqfrms-mbp/Documents/GitHub/umd-npm-package/src/export.js',
  loaded: false,
  children: [],
  paths: [
    '/Users/xgqfrms-mbp/Documents/GitHub/umd-npm-package/src/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/umd-npm-package/node_modules',
    '/Users/xgqfrms-mbp/Documents/GitHub/node_modules',
    '/Users/xgqfrms-mbp/Documents/node_modules',
    '/Users/xgqfrms-mbp/node_modules',
    '/Users/node_modules',
    '/node_modules'
  ],
  umd: { a: 1, b: 2, c: 3, d: 4 },
  export: { a: 1, b: 2, c: 3, d: 4 }
}
*/

https://nodejs.org/api/modules.html#modules_exports_shortcut

refs

http://www.ruanyifeng.com/blog/2015/05/require.html

Module System

https://www.cnblogs.com/xgqfrms/p/9493550.html

node --experimental-modules & node.js ES Modules

https://www.cnblogs.com/xgqfrms/p/13591967.html

---

---

©xgqfrms 2012-2025

www.cnblogs.com 发布文章使用：只允许注册用户才可以访问！

---