Interfaces are used to create reusable, modular types that describe the shape of objects. They serve almost the exact same purposes as type aliases with a slightly different syntax.

```ts
// Interface
interface Person = {
name: string
age: number
}

// Use interface in the annotation
const greetPerson = (person: Person) => {
    return `Hello, ${person.name}! You are ${person.age} years old.`;
}
```

 **Reopening Interfaces:** you can declare the same interface more than once, and TypeScript will merge all declarations together.
 
 ```ts
// Interface
interface Person = {
name: string;
}

interface Person = {
age: number;
}

const person: Person = {
  name: "Valentin",
  age: 100
};

```

**Extending interfaces** allows one interface to inherit the properties of another.

 ```ts
// Interface
interface Person = {
name: string;
age: number;
}


interface Employee  extends Person {
email: string
}

const person: Employee = {
  name: "Valentin",
  age: 100,
  email: valentin@gmail.com
};

```

**Multiple Inheritance**: typeScript lets an interface extend multiple interfaces , combining all their properties. 


 ```ts

interface Person = {
name: string;
age: number;
}


interface Employee   {
readonly id: number;
email: string
}

interface Engineer extends Person,Employee {
 level: string.
 languages: string[]
}

const person: Engineer = {
  id: 12345,
  name: "Valentin",
  age: 100,
  email: valentin@gmail.com,
  level: "Senior",
  languages: ["Javascript", "Typescript"]
};

```


Typescript Interfaces

Typescript Interfaces, reopening Interfaces, extending interfaces, multiple inheritance

Interfaces in typescript

Typescript Interfaces