type vs interface in TypeScript: Which to Use and When

In TypeScript there are two ways to describe types: type and interface.

Interface

• interface is used to describe the structure of objects and classes, as well as to extend other interfaces.

interface usage example:

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

interface Employee extends Person {
  position: string;
}

const employee: Employee = {
  name: "John",
  age: 30,
  position: "Developer"
};

interface allows using the extends keyword to extend other interfaces. This makes it convenient for working with object-oriented approach.

Type

• type is more universal and can be used not only for objects, but also for other data types such as primitives, unions, intersections and others.

type usage example:

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

type Employee = Person & {
  position: string;
};

const employee: Employee = {
  name: "John",
  age: 30,
  position: "Developer"
};

When to use interface or type?

• interface should be used when working with objects, especially if you need to extend or modify them using extends or implement in classes using implements.
• type should be used when you need to work with universal types such as unions, intersections, tuples and primitives.