# Object Types & Interfaces — TypeScript

Source: https://www.geekswithgeeks.com/en/typescript/ts-object-types-interfaces

> Describe the shape of an object, inline or with a reusable interface.

## Inline object types

You can annotate an object's shape directly, right where it's used.

```typescript
let user: { name: string; age: number } = {
  name: "Ada",
  age: 36,
};
user.age = "old";
// Error: Type 'string' is not assignable to type 'number'.
```

## Interfaces

An `interface` names a shape so you can reuse it across variables, parameters and return types.

```typescript
interface User {
  name: string;
  age: number;
}

function printUser(u: User): void {
  console.log(`${u.name} (${u.age})`);
}
```

## Why interfaces?

Any object with the right properties satisfies an interface — TS checks **structure**, not the class name. This is called "structural typing".