Lesson 6: Interfaces and Type Aliases

Interfaces

An interface describes the shape of an object and allows you to reuse the same definition in multiple places.

interface Student {
  name: string;
  age: number;
  grade: string;
}

let student1: Student = {
  name: "Ali",
  age: 20,
  grade: "A"
};

Optional and Readonly Properties

interface User {
  name: string;
  email?: string;
  readonly id: number;
}

Type Aliases

Type aliases can also name object structures, but they are especially useful for unions and tuples.

type Status = "Open" | "Closed" | "Pending";
type Point = [number, number];

When to Use Each

• Use interface mainly for object structures.
• Use type for unions, tuples, and combined types.

Summary

Interfaces and type aliases help you organize data structures in a reusable way. They are essential tools for clean and scalable TypeScript code.