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CommonJS vs ESM

Learn the difference between CommonJS (require) and ES modules.

CommonJS vs ESM

Node.js has two module systems: CommonJS (old) and ES modules (modern). ESM is recommended in Node.js 22.

In CommonJS, you export with module.exports and import with require. In ESM, you use export and import.

Mixing the two in one project causes errors; you select ESM by setting "type": "module" in package.json. You may see CommonJS in old code, but use ESM in new code.

Which should you choose?

When starting a new project, choosing ESM is recommended. If you add "type": "module" to package.json, all your .js files are treated as ESM.

If you are maintaining an old project that uses require, staying with CommonJS may be the consistent choice. Still, prefer ESM for new additions.

Do not mix the two systems in the same file; it is confusing and leads to errors.

Practice Write an ESM import

Import the greet function from ./hello.js. Then call console.log with greet('World').

Starter code

index.js
// Import greet from ./hello.js
// Then call greet('World') and log it

Sample solution

index.js
import { greet } from "./hello.js";

console.log(greet("World"));

Expected output

Hello, World

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Import with require

Question 
CommonJS: const fs = ____("fs");
Answer 
CommonJS: const fs = require("fs");

Explanation: CommonJS uses require.

2 What does "type": "module" do?

  • Deletes all .js files
  • Recognizes only .mjs files
  • Disables npm commands
  • Treats all .js files as ESM Correct answer

Explanation: type: module treats .js files as ESM.

3 Match the module systems

Term Meaning
require CommonJS import
import ESM import
module.exports CommonJS export
export ESM export

All lessons in Beginner

1 Node.js basics

  1. What is Node.js?
  2. Your first program
  3. ES modules
  4. package.json
  5. CommonJS vs ESM
  6. Summary - Node.js basics

2 Variables

  1. let and const
  2. var and scope
  3. Type inference
  4. Destructuring
  5. Spread and rest
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Template literals
  3. Number and Math
  4. Symbol
  5. typeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. process.argv
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Nullish coalescing
  6. Summary - Operators

6 Strings

  1. String methods
  2. String search
  3. substring and slice
  4. replace and split
  5. padStart and trim
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Ternary
  5. Optional chaining
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. for...of
  4. for...in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. push and pop
  4. shift and unshift
  5. splice and slice
  6. Summary - Arrays

11 Array methods

  1. map
  2. filter
  3. reduce
  4. find and some
  5. forEach
  6. Summary - Array methods

12 Objects

  1. Object literal
  2. Property access
  3. Computed properties
  4. Object methods
  5. Object spread
  6. Summary - Objects

13 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Default parameters
  5. Rest parameters
  6. Summary - Functions

14 Callbacks

  1. What are callbacks?
  2. Higher-order functions
  3. forEach with callbacks
  4. Error-first callbacks
  5. Callback hell
  6. Summary - Callbacks

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Promises

  1. What are promises?
  2. then and catch
  3. Promise.all
  4. Promise.race
  5. finally
  6. Summary - Promises

17 async/await

  1. async function
  2. await
  3. try/catch
  4. await with Promise.all
  5. Sequential await
  6. Summary - async/await

18 fs module

  1. fs.promises
  2. readFile
  3. writeFile
  4. appendFile
  5. existsSync
  6. Summary - fs module

19 path module

  1. path.join
  2. path.resolve
  3. path.parse
  4. path.dirname and basename
  5. path.extname
  6. Summary - path module

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. fs persistence
  5. Putting it together