📚 ESM vs CommonJS

🔍 Overview

• CommonJS (CJS):
  Introduced in 2009, it became the default module system for Node.js, using require() for imports and module.exports for exports.

• ESM (ECMAScript Modules):
  Standardized in ECMAScript 6 (2015), ESM uses import and export statements, aiming for a more modern and flexible module system.

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⚙️ Syntax & Usage

Feature	CommonJS	ESM
Import	const x = require('x')	import x from 'x'
Export	module.exports = x	export default x
Named Export	exports.x = x	export { x }
Dynamic Import	require()	import() (async)

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🚀 Loading Mechanism

• CommonJS:
  Modules are loaded synchronously, which can be blocking and less efficient, especially in a client-side environment.

• ESM:
  Supports asynchronous loading, allowing for non-blocking operations and better performance in modern applications.

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🔄 Compatibility & Interoperability

• CommonJS:
  Primarily used in Node.js; not natively supported in browsers without bundling tools.

• ESM:
  Natively supported in modern browsers and Node.js (v12+), facilitating isomorphic JavaScript applications.

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📦 Performance & Optimization

• CommonJS:
  Lacks static analysis, making it challenging for tools to optimize code (e.g., tree shaking).

• ESM:
  Supports static analysis, enabling optimizations like tree shaking to reduce bundle sizes and improve performance.

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🧩 Use Cases & Recommendations

• Use CommonJS:

  • For existing Node.js projects without a build process.
  • When backward compatibility with older Node.js versions is required.

• Use ESM:

  • For new projects aiming for modern JavaScript standards.
  • When targeting both client-side and server-side environments.
  • To take advantage of features like static analysis and tree shaking.

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✅ Conclusion

In the modern JavaScript ecosystem, ESM is generally the preferred choice due to its standardization, better performance characteristics, and compatibility with both browsers and Node.js.

However, CommonJS remains relevant for legacy Node.js applications and scenarios where its synchronous loading model is beneficial.

👉 For new projects, especially those targeting cross-platform compatibility and optimized performance, adopting ESM is advisable.