16 — Modules & Namespaces

Core Concepts

• ES Modules — import/export syntax (the modern standard)
• Named exports — export function fn(), export { a, b }
• Default exports — export default class Foo
• Re-exports — export { fn } from "./module" barrel files
• Dynamic imports — const mod = await import("./module") code splitting
• Namespaces — namespace Foo { } legacy TS-specific grouping
• Module augmentation — extend existing module types
• Side-effect imports — import "./polyfill" just run the module

Module Best Practices

• Use named exports (better tree-shaking, autocomplete)
• Use barrel files (index.ts) sparingly (can hurt tree-shaking)
• Prefer ES modules over namespaces in modern code
• Use type imports for type-only imports: import type { User } from "./types"