There are two main tools to declare the shape of an object: interfaces and type aliases. They are very similar, and for the most common cases act the same.

type BirdType = {
  wings: 2;
};

interface BirdInterface {
  wings: 2;
}

const bird1: BirdType = { wings: 2 };
const bird2: BirdInterface = { wings: 2 };

// Because TypeScript is a structural type system, it's possible to intermix their use too.

const bird3: BirdInterface = bird1;

// They both support extending other interfaces and types. Type aliases do this via intersection types, while interfaces have a keyword.

type Owl = { nocturnal: true } & BirdType;
type Robin = { nocturnal: false } & BirdInterface;

interface Peacock extends BirdType {
  colourful: true;
  flies: false;
}
interface Chicken extends BirdInterface {
  colourful: false;
  flies: false;
}

let owl: Owl = { wings: 2, nocturnal: true };
let chicken: Chicken = { wings: 2, colourful: false, flies: false };

// That said, we recommend you use interfaces over type aliases. Specifically, because you will get better error messages. If you hover over the following errors, you can see how TypeScript can provide terser and more focused messages when working with interfaces like Chicken.

owl = chicken;
chicken = owl;

// One major difference between type aliases vs interfaces are that interfaces are open and type aliases are closed. This means you can extend an interface by declaring it a second time.

interface Kitten {
  purrs: boolean;
}

interface Kitten {
  colour: string;
}

// In the other case a type cannot be changed outside of its declaration.

type Puppy = {
  color: string;
};

type Puppy = {
  toys: number;
};

// Depending on your goals, this difference could be a positive or a negative. However for publicly exposed types, it's a better call to make them an interface. One of the best resources for seeing all of the edge cases around types vs interfaces, this stack overflow thread is a good place to start: https://stackoverflow.com/questions/37233735/typescript-interfaces-vs-types/52682220#52682220