Node.js require 模块加载原理 All In One

时间：2022-06-09 06:26:13

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

Node.js require 模块加载原理 All In One

"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

Node.js require 模块加载原理 All In One

Node.js require 模块加载原理 All In One

Node.js require 模块加载原理 All In One

xgqfrms 2012-2020

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