Module Traps

CommonJS

• exports = x breaks — must use module.exports = x (exports is just reference)
• require() cached — same object returned, mutations visible everywhere
• Circular deps return incomplete export — whatever was assigned at require time

ESM

• No __dirname — use fileURLToPath(import.meta.url) + dirname()
• Can't require() ESM from CJS — must use dynamic import() which returns Promise
• import is hoisted — runs before other code, can't conditionally import

Interop

• ESM importing CJS — only default import works, no named exports
• "type": "module" affects all .js — use .cjs extension for CommonJS files