In real applications, data is not always fixed. Sometimes a value can have more than one type, or certain fields may not always be present.

TypeScript allows you to handle these cases using union types and optional properties.

Union Types

A union type allows a variable to hold more than one type:

let id: string | number;

id = 10;
id = "abc123";

This is useful when a value can come in different formats.

Optional Properties

Sometimes an object may have properties that are not always required.

You can mark them as optional using ?:

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

Now the age property can be included or omitted:

let user1: User = { name: "Alice", age: 30 };
let user2: User = { name: "Bob" };

Combining Both

You can use union types and optional properties together:

type Order = {
  id: number | string;
  status?: string;
};