Typescript interfaces

In typescript, interfaces are implicit -- any object that satisfies the requested interface is allowed.
Interfaces can be extended (grown) into new interfaces that include others.

Interface

interface Person {
    firstName: string;
    lastName: string;
}

interface Employee extends Person {
    id: number;
}

Type Alias

You can also define a type-alias, but you cannot extend it in a new interface.

type Point {
    x: number;
    y: number;
}