TypeScript - Declaration Files (.d.ts)

What are declaration files?

.d.ts files describe types for code whose implementation may be JS or TS. They enable consumers to get IntelliSense and compile-time checks.

Example

// index.d.ts
export interface Options { retries?: number }
export declare function request(url: string, opts?: Options): Promise;

Publishing

• Set "types": "dist/index.d.ts" in package.json.
• Enable declaration and declarationMap in tsconfig to emit types from TS sources.

Ambient declarations

declare global { interface Window { myGlobal: number } }
export {}; // make this a module