Type Aliases

Give a Type a Name

Writing the same object type again and again is tiring. A type alias gives it a name with the type keyword. By convention the name is PascalCase.

Example

This is the start of our ShopEase e-commerce model used throughout the course.

type Category = "Electronics" | "Books" | "Fashion";

type Product = {
  id: number;
  name: string;
  description: string;
  price: number;
  stock: number;
  category: Category;
};

const laptop: Product = {
  id: 1,
  name: "ShopEase Laptop 14",
  description: "Thin and light",
  price: 54999,
  stock: 12,
  category: "Electronics",
};

function isAvailable(p: Product): boolean {
  return p.stock > 0;
}

console.log(laptop.name, isAvailable(laptop));

Output

ShopEase Laptop 14 true

Aliases for Any Type

Example

An alias can name any type, not just objects: primitives, unions, tuples, functions.

type ProductId = number;
type Price = number;
type Point = [x: number, y: number];
type Formatter = (amount: Price) => string;

const id: ProductId = 42;
const origin: Point = [0, 0];
const inr: Formatter = (amount) => "Rs. " + amount.toLocaleString("en-IN");

console.log(id, origin, inr(1250000));

Output

42 [ 0, 0 ] Rs. 12,50,000

Note: An alias does not create a new type. ProductId and number are interchangeable. (Branded types in the advanced level fix that.)

Combining Types with &

Example

An intersection A & B has all properties of both.

type Timestamps = { createdAt: string; updatedAt: string };
type User = { id: number; name: string; email: string };
type UserRecord = User & Timestamps;

const u: UserRecord = {
  id: 7, name: "Arjun", email: "[email protected]",
  createdAt: "2026-01-15T10:00:00Z", updatedAt: "2026-02-01T09:30:00Z",
};
console.log(Object.keys(u).join(", "));

Output

id, name, email, createdAt, updatedAt