Package design

Set up a multi-file library skeleton.

Package design

A library package is usually built on a multi-file skeleton. Each file has a single responsibility: types, helper functions, and the entry point live in separate files. The src/index.ts file is the public door of the package and combines other modules.

src/
  types.ts      // type definitions
  helpers.ts    // helper functions
  index.ts      // entry point

Module structure

Each file is a module; values are exported with export and imported with import. The tsconfig.json sets compilation options and the output directory. This way, compiling the package produces a single dist/ folder.

// types.ts
export interface Book { name: string; }
// index.ts
export { Book } from "./types";

Exercise Book interface and add function

Define an interface named Kitap with a property ad: string. The function kitapEkle takes a title: string parameter and returns { ad: title } of type Kitap. Print kitapEkle("TypeScript").ad with console.log.

Show example solution

interface Kitap {
  ad: string;
}
function kitapEkle(title: string): Kitap {
  return { ad: title };
}
console.log(kitapEkle("TypeScript").ad);

Test yourself

What is the role of index.ts in a library package?
- Contains only type definitions
- Contains no runtime code
- Replaces tsconfig.json
- Combines modules as the package entry point
Show answer

Combines modules as the package entry point — index.ts is the package entry point; it imports other modules and re-exports them as a single API.

Export keyword

// types.ts
____ interface Kitap { ad: string; }

Show answer

// types.ts
export interface Kitap { ad: string; }

Package parts

src/types.ts

Type definitions
src/helpers.ts

Helper functions
src/index.ts

Entry point
tsconfig.json

Compilation settings

Next lesson: Exporting types

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