Node.js模块加载的不同机制有哪些？求专业解答

Hey there! Great question — I totally get why this might be confusing, since Node.js has evolved its module system over time. The three distinct module loading mechanisms you’re hearing about are:

1. CommonJS (CJS) — The Original Workhorse #

This is the module system Node.js launched with, and it’s still the default for .js files unless you configure otherwise.

• Uses require() to pull in modules, and module.exports or exports to expose functionality from your own modules
• Loads modules synchronously, which works well for server-side initialization where a brief block during startup isn’t a problem
• Modules are cached after the first load, so repeated require() calls for the same module return the exact same instance
• Example code:

  // Importing a built-in CJS module
  const fs = require('fs');
  // Exporting from a custom module
  module.exports = {
    greet: (name) => `Hello, ${name}!`
  };
  

2. ECMAScript Modules (ESM) — The Standardized Modern Approach #

Node.js added support for ES6+ modules to align with browser JavaScript and modern JS standards.

• Uses import and export syntax instead of require()/module.exports
• Supports asynchronous loading, which is more flexible for dynamic or non-blocking use cases
• To enable ESM in your project, you can either:
  • Rename files to use the .mjs extension
  • Add "type": "module" to your root package.json
• Example code:

  // Importing a module (using promises for async fs)
  import { readFile } from 'fs/promises';
  // Exporting a function
  export const double = (num) => num * 2;
  

• ESM has stricter syntax rules (no require() by default, no implicit file extensions) and a different caching model than CJS.

3. Specialized Native & Static Module Loaders #

This third category covers modules that don’t fit neatly into the CJS/ESM paradigm, including:

• JSON Modules: Node.js can directly load .json files using either require() (CJS) or import (ESM), no manual parsing needed. Example: const config = require('./config.json')
• C++ Addons: These are native modules written in C++ that compile to platform-specific binaries. They’re loaded via require() just like CJS modules, and are used for performance-critical tasks or accessing low-level system APIs.
• Built-in Modules: Node.js’s core modules (like fs, http) are optimized and loaded directly from the Node.js runtime, not from the filesystem. They work seamlessly with both CJS and ESM syntax.

内容的提问来源于stack exchange，提问作者Hemadri Dasari