Type Aliases

Type Aliases

Type aliases let you create custom names for types, making complex types reusable and readable.

Basic Type Alias

type StringOrNumber = string | number;

let uid: StringOrNumber;
uid = "abc";  // ✅
uid = 123;    // ✅

Object Type Alias

type User = {
    name: string;
    age: number;
    id: StringOrNumber;
};

const userOne: User = { name: "Mario", age: 30, id: "abc" };
const userTwo: User = { name: "Luigi", age: 28, id: 456 };

Type Aliases with Functions

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

const greet = (user: User): string => {
    return `Hello ${user.name}, age ${user.age}`;
};

Intersection Types

type HasName = { name: string };
type HasAge = { age: number };
type Person = HasName & HasAge;

const person: Person = { name: "Mario", age: 30 };

Key Takeaways

• type keyword creates reusable type aliases
• Use them for union types, object shapes, and more
• Intersection types (&) combine multiple types
• Makes code DRY and easier to maintain