Lesson 17 — Utility types

Build new types from old ones

TypeScript ships utility types that transform a type you already have. Partial<T> makes every property optional — perfect for "change only some fields" updates. Pick<T, "a" | "b"> keeps only the listed properties. Others include Omit, Readonly and Record.

interface Post { title: string; body: string; likes: number }
type PostPreview = Pick<Post, "title">;   // { title: string }
type PostEdit = Partial<Post>;            // every field optional

Why it matters: you derive types instead of copying them, so they never drift apart.