Branded Types
type UserId = string & { readonly __brand: "UserId" };type PostId = string & { readonly __brand: "PostId" };function createUserId(id: string): UserId { return id as UserId; }function getUser(id: UserId) { /* ... */ }const userId = createUserId("abc-123");getUser(userId); // WorksgetUser("xyz" as PostId); // Compile error!Template Literal Types
type HTTPMethod = "GET" | "POST" | "PUT" | "DELETE";type Endpoint = "/users" | "/posts";type Route = `${HTTPMethod} ${Endpoint}`;// "GET /users" | "GET /posts" | ... (8 combinations)Conditional Types
type Unwrap<T> = T extends Promise<infer U> ? U : T;type Result = Unwrap<Promise<string>>; // stringUtility Types You Should Know
Partial<T> — all properties optional
Required<T> — all properties required
Pick<T, K> — extract subset
Omit<T, K> — remove properties
Record<K, V> — key-value types
ReturnType<F> — extract return type