Union & Intersection

Union and intersection types give you the power to describe complex data relationships. Union types (`|`) let you say "this could be one of these types," while intersection types (`&`) let you combine multiple types into one. These are essential for building robust type systems that accurately reflect your application's data structures.

Union and Intersection Types

Use union types when a value can be one of several different types, like a user's status that could be "active", "inactive", or "pending". Intersection types come in handy when you need to combine multiple type requirements, like creating a User object that has both an ID and authentication properties.

// Union types
let status: "active" | "inactive" | "pending" = "active";
let id: string | number = "user123";

// Type narrowing with typeof
function processValue(value: string | number) {
    if (typeof value === "string") {
        return value.toUpperCase();
    } else {
        return value * 2;
    }
}

// Intersection types
interface BaseUser {
    id: number;
    name: string;
}

interface AdminUser {
    permissions: string[];
    role: "admin";
}

type FullUser = BaseUser & AdminUser;
const admin: FullUser = { id: 1, name: "Bob", permissions: ["read", "write"], role: "admin" };