CommonJS Modules
📌 Covered in this chapter:
require() · module.exports · Module Scope · Module Caching · Circular Dependencies
Understand Node.js's original module system: require(), module.exports, and how modules are scoped and cached.
1CommonJS Modules — What You'll Learn
Understand Node.js's original module system: require(), module.exports, and how modules are scoped and cached.
Here's everything this chapter covers, in the order you'll learn it:
- What a module is and why they're needed
- require() to import a module
- module.exports to export functionality
- Exporting functions
- Exporting objects
- Importing built-in modules
- Module scope (each file is isolated by default)
- Module caching (a module runs once, then is cached)
- Circular dependencies and how to avoid them
2Working Example
💻 Example: CommonJS Modules
JavaScript
▶ Run in Compiler
// math.js
function add(first, second) {
return first + second;
}
module.exports = { add };💻 Continued Example
JavaScript
▶ Run in Compiler
// app.js
const { add } = require("./math");
console.log(add(10, 20));3Best Practices & Common Pitfalls
💡 Key things to remember:
- CommonJS is the original, default module system in Node.js and is still extremely common in existing codebases.
- require() calls are synchronous, which is fine for local files but not ideal for network requests.
❓ Frequently Asked Questions (FAQ)
Q What's the most important thing to understand about commonjs modules?
Focus on: require() · module.exports · Module Scope · Module Caching · Circular Dependencies. These are the core building blocks this chapter's examples are built around, and they show up repeatedly in later chapters of this course.
Q Do I need external npm packages for commonjs modules?
Only where explicitly shown in the code examples above (like Express, Zod, or Socket.IO) — otherwise, this chapter relies entirely on Node.js's own built-in capabilities.