TypeScript Academy · Lesson

Interface Extension and Merging

Extend interfaces and understand declaration merging.

Welcome

Interfaces can extend other interfaces to build on existing shapes, and TypeScript merges multiple declarations of the same interface automatically.

Use the `extends` keyword to create a new interface that includes all properties from the parent.

interface Animal { name: string; }
interface Dog extends Animal {
  breed: string;
}
const rex: Dog = { name: 'Rex', breed: 'Labrador' };