JavaScript has undergone significant transformations since its inception, with one of the most noteworthy developments being the introduction of modular JavaScript. Within this, two major approaches have become prominent: CommonJS and ES Modules.
However, comprehending the distinctions between these two methodologies can be perplexing, especially for developers new to the modular JavaScript domain.
In this article, we’ll explore CommonJS and ES Modules in-depth, shedding light on their origins, key features, pros, cons, and the critical differences between these module systems.
CommonJS is a highly functional and effective module system that is used for server-side development in Node.js. It was specifically designed to solve the complex problem of organizing code in large and intricate projects.
CommonJS operates on a set of principles that enable developers to write code that can be reused and easily managed. It also provides an excellent mechanism to manage dependencies for code, even in the most challenging situations.
It is a reliable and powerful tool that can greatly enhance the development process, especially in the case of large-scale projects. Overall, CommonJS is an excellent choice for developers who want to write top-quality, scalable, reusable, and easily manageable code.
CommonJS was developed in 2009 by Kevin Dangoor and other developers. It was created to solve the problem of managing dependencies in JavaScript projects. Before CommonJS, JavaScript code was typically written in a single file, making it difficult to manage dependencies.
CommonJS is a synchronous module system. This means that when a module is imported, the code execution is blocked until the module is loaded. The module system uses the require function to import modules and the module.exports object to export modules.
To illustrate how CommonJS works, let’s consider a practical example involving a logger and app module.
The logger.js module defines a simple logging function that appends a timestamp to each message. It then exports this function for use in other modules.
// logger.js
function log(message) {
const timestamp = new Date().toISOString();
console.log(`${timestamp}: ${message}`);
}
module. Exports = log; The app.js imports the logging function from logger.js and uses it to log various messages, demonstrating how code is shared and reused across modules.
// app.js
const log = require('./logger');
log("Starting the application...");
// Additional application logic.
log("Application is running");
// More application logic.
log("Application finished execution"); Explanation
The logger.js exports a log function, a typical CommonJS pattern for making code available to other modules. The app.js demonstrates how to import and use the exported log function from logger.js.
ES Modules is a modern module system that is built into the JavaScript language. ES Modules was created to solve the problem of managing dependencies in JavaScript projects, both on the client-side and server-side.
ES Modules was introduced in ECMAScript 6 in 2015. It was created to provide a standardized way to modularize JavaScript code. ES Modules is now widely supported by modern web browsers and Node.js.
ES Modules represents a more modern approach to JavaScript module management, using an asynchronous model for loading modules. Let’s see this in action through a practical example.
The logger.mjs module provides a logging function that outputs a message with a timestamp. It uses the ES Modules export syntax to make the function available to other modules.
// logger.mjs
export function log(message) {
const timestamp = new Date().toISOString();
console.log(`${timestamp}: ${message}`);
} The app.mjs module demonstrates how to import the log function from the logger.mjs module and use it within the app, showcasing the ES Modules import syntax.
// app.mjs
import { log } from './logger.mjs';
log("Starting the application...");
// Additional application logic.
log("Application is running");
// More application logic.
log("Application finished execution"); Explanation
In logger.mjs, the log function is exported using the export keyword. This is a standard method for exposing functionality in ES Modules. The app.mjs imports the log function using the import { log } from the ‘./logger.mjs’ syntax. This shows how ES Modules allows for the selective importing of specific functions or variables from other modules.
The primary difference between CommonJS and ES Modules is the module loading system. CommonJS uses synchronous loading, while ES Modules uses asynchronous loading. Additionally, CommonJS uses the require function to import modules, while ES Modules uses the import statement.
A second significant difference is the way modules are cached. In CommonJS, once a module is loaded, it is cached in memory, and subsequent requests for the same module return the cached version. In contrast, ES Modules does not cache modules by default. This can lead to additional network requests for the same module.
Another significant difference between CommonJS and ES Modules is how they handle exports. CommonJS typically uses the module.exports object to export modules. This distinction in export mechanisms is essential to understand when working with these module systems, as it impacts how you structure and use your code.
CommonJS relies on an object-based approach, while ES Modules provides a more explicit and flexible exporting mechanism. This can be especially relevant when dealing with complex projects and interoperability between different module systems.
The CommonJS is ideal for:
Some of the examples of apps that use CommonJS are:
The ES Modules is suitable for:
Some examples of apps that use ES Modules are:
Developers should consider factors such as their target platform, the level of front-end or back-end complexity, and the need for dynamic imports when choosing between CommonJS and ES Modules.
When starting a new project, it is often better to use ES Modules, since it has been standardized for many years. It has stable support in NodeJS and is interoperable with CommonJS. ES Modules support has also been added to many libraries by new package maintainers.
On the other hand, if you are maintaining an existing NodeJS project using CommonJS or using an older version of Node.js, it is better to stick with CommonJS. NodeJS still uses CommonJS as its default module system and is unlikely to change any time soon. A conversion to ES Modules would also make the app incompatible with earlier versions of Node.js because of the sketchy support.
Thanks for reading! CommonJS and ES Modules are two popular module systems in JavaScript. Each has its own set of advantages and disadvantages. Choosing the right module system depends on the specific needs of your app. By understanding the differences between CommonJS and ES Modules, developers can make informed decisions and choose the best module system for their needs.
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