CommonJS vs ES Modules
In the vast world of JavaScript, especially in server environments like Node.js, module management is crucial for organizing and reusing code. Historically, Node.js adopted a module system called CommonJS. However, with the evolution of the JavaScript standard, ES Modules (ECMAScript modules) emerged as the official way to manage modules in the language. Understanding their differences is fundamental for developing modern applications.
Synopsis:
Although both systems serve the same function of allowing you to split your code into separate, reusable files, their syntax and behavior differ.
- 1. CommonJS (Traditional Node.js):
It is the default module system in Node.js since its inception. It uses the require() function to import modules and module.exports or exports to export values.
- 2. ES Modules (JavaScript Standard):
They are the official JavaScript standard for importing and exporting modules. They use the import and export keywords. They are the future of modularity in JavaScript.
Key Differences and When to Use Each:
- Syntax: As seen above, syntax is the most obvious change. CommonJS uses require/module.exports while ES Modules use import/export.
- Module Loading:
- CommonJS: Module loading is synchronous. This means that when you call require(), the code stops until the module is fully loaded.
- ES Modules: Module loading is asynchronous. This allows for better performance in the browser and facilitates optimizations like "tree-shaking" (elimination of unused code).
- Import/Export:
- CommonJS: Exports a single object (what module.exports or exports points to). You can destructure it after importing.
- ES Modules: Allows named exports (`export const`) and a default export (`export default`).
- this Context: In CommonJS, this inside an exported module refers to module.exports. In ES Modules, this is undefined at the top level of the module.
- Compatibility:
- CommonJS: It is the original module system for Node.js and is still widely used, especially in older projects or libraries that were created with it.
- ES Modules: It is the modern standard. Node.js has been improving its support for ES Modules. To use them, you generally need files with the .mjs extension or to set "type": "module" in your package.json.
In new Node.js projects, it is recommended to use ES Modules whenever possible, as they are the language standard and offer benefits like "tree-shaking" and better interoperability with frontend development. However, in practice, you will often find yourself working with projects that use CommonJS, so it is vital to know both.
Exercises
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