Modules

Export and import names

Use ES module syntax. Compile with a module setting that matches your runtime.

// math.ts
export function square(n: number): number {
  return n * n;
}

// app.ts
import { square } from "./math";
console.log(square(4));

Default exports

A file may have one default export. Named exports are easier to rename safely.

// greeter.ts
export default function greet(name: string) {
  return `Hi, ${name}`;
}

// app.ts
import greet from "./greeter";
console.log(greet("TypeScript"));

Compile multiple files

With a tsconfig.json, run tsc once for the whole project.

tsc
node dist/app.js

Module habits

• Keep one clear idea per file
• Prefer named exports for libraries and shared utilities
• Match module in tsconfig to Node ESM/CJS or bundlers
• Avoid circular imports between modules