Built-in Utility Types
TypeScript provides globally available utility types to transform existing types easily without rewriting code.
1. Object Transformation Utilities
| Utility Type | Description | Code Syntax Example |
|---|---|---|
Partial<T> | Makes all properties in T optional | type DraftUser = Partial<User>; |
Required<T> | Makes all properties in T required | type StrictUser = Required<User>; |
Readonly<T> | Makes all properties in T immutable | type ImmutableUser = Readonly<User>; |
Pick<T, K> | Selects specific keys K from T | type UserPreview = Pick<User, "name" | "email">; |
Omit<T, K> | Removes specific keys K from T | type UserWithoutPassword = Omit<User, "password">; |
Record<K, T> | Constructs an object with key K and value T | type UserMap = Record<string, User>; |
2. Live Code Example: `Partial` & `Omit`
interface User {
id: number;
name: string;
email: string;
role: string;
}
// 1. Partial: Useful for Update API payloads
function updateUser(id: number, fieldsToUpdate: Partial<User>) {
// fieldsToUpdate allows optional { name?, email?, role? }
}
updateUser(101, { email: "newemail@example.com" });
// 2. Omit: Useful for Create User DTOs (where id is auto-generated)
type CreateUserDTO = Omit<User, "id">;
const newUser: CreateUserDTO = {
name: "Bob",
email: "bob@example.com",
role: "User"
};3. Union Filtering (`Extract` & `Exclude`)
type Event = "click" | "hover" | "scroll" | "mousemove"; // Exclude "mousemove" from Event union type NonMouseEvents = Exclude<Event, "mousemove">; // "click" | "hover" | "scroll" // Extract only "click" | "hover" type InteractiveEvents = Extract<Event, "click" | "hover">;
Next Up
Explore advanced Mapped Types (`[K in keyof T]`) and Conditional Types (`infer`).
Next Lesson: Mapped & Conditional Types →
