UNDERSTANDING NODE.JS MODULES: COMMONJS VS. ES MODULES

Understanding Node.js Modules: CommonJS vs. ES Modules

Understanding Node.js Modules: CommonJS vs. ES Modules

Blog Article

If you're learning Node.js or working on JavaScript projects, you've probably come across two different ways to use code from other files: require and import. These two methods come from two different module systems—CommonJS and ES Modules.

This article will help you understand what modules are, the difference between these two systems, and how to choose the right one for your project—all without confusing technical jargon.

 

What Are Modules?


Modules are just individual files that contain code you want to reuse. Instead of putting everything into one massive file, developers split their code into smaller pieces. For example, you might have one file that handles math functions, another that connects to a database, and another that starts your app.

Using modules makes code cleaner, easier to manage, and reusable. To share and use code between files, you need a way to export code from one file and import it into another. That’s where module systems come in.

 

CommonJS: The Traditional Way


CommonJS is the original module system in Node.js. It uses the require keyword to bring in code from another file, and module.exports to share it.

Imagine you create a file called math.js that contains a function to add two numbers. You can then load that function into another file using require.

This system has been around since Node.js was first released, and it works in all versions of Node. Most older packages you find on npm (Node’s package manager) use this format.

 

ES Modules: The Modern Way


ES Modules (often called ESM) is the newer, official module system introduced in modern JavaScript. It uses the import and export keywords instead of require and module.exports.

This system is now used in web browsers and is supported in Node.js starting from version 12, becoming stable in version 14 and above.

To use ES Modules in Node.js, you have two options:

  1. Use the .mjs file extension.


  2. Use the .js extension but add this line to your package.json file: "type": "module"



Once you do that, Node will understand that you’re using ES Modules.

 

How They Differ


Let’s look at a few ways CommonJS and ES Modules are different:

  • Syntax: CommonJS uses require and module.exports. ES Modules use import and export.


  • Support: CommonJS is supported by default in Node.js. ES Modules need to be enabled.


  • File Types: CommonJS uses .js files. ES Modules use either .mjs, or .js files with extra configuration.


  • How They Load: CommonJS loads modules one line at a time (synchronously). ES Modules can load in a more flexible, async-friendly way.


  • Browser Compatibility: ES Modules work directly in modern web browsers. CommonJS does not.



 

Why Are There Two Systems?


Originally, JavaScript was only used in browsers, and there was no built-in way to manage modules. When Node.js came along, it introduced CommonJS to solve this problem.

Later, the JavaScript language itself added a standard way to use modules, which became ES Modules. Now, modern browsers and tools like Node.js support ES Modules to make JavaScript more consistent across platforms.

So, Node.js supports both systems to remain compatible with older code (CommonJS) while also supporting the new standard (ESM).

 

Which One Should You Use?


Here’s a simple guide to help you decide:

  • If you're working on a new project and want to keep up with modern standards, use ES Modules.


  • If you're working with older Node.js packages or tools that still use require, use CommonJS for compatibility.


  • If your project runs in both Node.js and browsers, ES Modules is the better choice.



That said, both systems are widely used and accepted. You won’t go wrong using either, as long as you stay consistent within your project.

If you're building apps professionally or offering Node.js Development Services, it’s a good idea to understand both systems so you can adapt to whatever structure a client’s project uses.


In Summary


Modules help you organize and reuse your code. Node.js supports two module systems:

  • CommonJS: The older system that uses require and works by default.


  • ES Modules: The modern system that uses import and needs a little setup.



Understanding the difference helps you write cleaner, more maintainable code and avoid headaches when switching between projects or collaborating with others.

Whether you go with require or import, the most important thing is knowing how and why each system works—so you can pick the best one for your needs.

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