The differences between CommonJS (CJS) and ECMAScript Modules (ESM) in JavaScript primarily revolve around their loading mechanisms, syntax, and usage contexts. Here are some key distinctions:
1. Module Loading Mechanism
CommonJS: Modules are loaded synchronously, meaning the code execution blocks until the module is fully loaded. This is particularly useful in server-side environments like Node.js where the performance impact of synchronous loading is mitigated by the nature of I/O operations which are also synchronous[1][5].
ECMAScript Modules: ESM supports asynchronous loading, allowing modules to be loaded in parallel. This non-blocking behavior is advantageous in browser environments, enhancing performance by not waiting for a module to load before continuing with the execution of other scripts[1][5].
2. Syntax
CommonJS: Uses the require() function to load modules and module.exports to export modules. For example:
ECMAScript Modules: Utilizes the import and export statements, providing a more declarative approach. For example:
import library from 'library';
export function myFunction() {}
This syntax is statically analyzable, meaning tools and compilers can optimize the code by analyzing imports and exports without executing it[1][4].
3. Interoperability
CommonJS: Primarily designed for use in Node.js and does not have native support in browsers without the use of bundlers like Webpack or Browserify[1].
ECMAScript Modules: Part of the ECMAScript standard and natively supported in modern browsers. ESM can also be used in Node.js, making it versatile for both server-side and client-side development[1][2].
4. Performance Optimization
CommonJS: Does not support tree shaking, a performance optimization technique used to remove unused code[1].
ECMAScript Modules: Supports tree shaking, allowing for smaller bundle sizes in production environments, which is crucial for performance in web applications[1][4].
