typescript-utility-types

TypeScript Utility Types

Master TypeScript's powerful type system including built-in utility types, mapped types, conditional types, and advanced type manipulation techniques for creating flexible, type-safe code.

Built-in Utility Types

Partial and Required

interface User {
  id: string;
  name: string;
  email: string;
  age: number;
}

// Partial makes all properties optional
type PartialUser = Partial<User>;
// { id?: string; name?: string; email?: string; age?: number; }

function updateUser(id: string, updates: Partial<User>): User {
  const existingUser = getUser(id);
  return { ...existingUser, ...updates };
}

updateUser('123', { name: 'John' }); // Valid
updateUser('123', { age: 30 }); // Valid

// Required makes all properties required
interface OptionalConfig {
  host?: string;
  port?: number;
  timeout?: number;
}

type RequiredConfig = Required<OptionalConfig>;
// { host: string; port: number; timeout: number; }

function validateConfig(config: Required<OptionalConfig>): boolean {
  return config.host.length > 0 && config.port > 0;
}

Pick and Omit

interface Article {
  id: string;
  title: string;
  content: string;
  author: string;
  createdAt: Date;
  updatedAt: Date;
  views: number;
}

// Pick selects specific properties
type ArticlePreview = Pick<Article, 'id' | 'title' | 'author'>;
// { id: string; title: string; author: string; }

function displayPreview(article: ArticlePreview): void {
  console.log(`${article.title} by ${article.author}`);
}

// Omit removes specific properties
type ArticleWithoutDates = Omit<Article, 'createdAt' | 'updatedAt'>;
// { id: string; title: string; content: string; author: string; views: number; }

// Combining Pick and Omit
type ArticleMetadata = Pick<Article, 'id' | 'author' | 'createdAt'>;
type ArticleData = Omit<Article, 'id' | 'createdAt' | 'updatedAt'>;

Readonly and Record

// Readonly makes all properties readonly
type ReadonlyUser = Readonly<User>;

const user: ReadonlyUser = {
  id: '1',
  name: 'John',
  email: '[email protected]',
  age: 30,
};

// user.name = 'Jane'; // Error: Cannot assign to 'name' because it is a read-only property

// Deep readonly for nested objects
type DeepReadonly<T> = {
  readonly [P in keyof T]: T[P] extends object
    ? DeepReadonly<T[P]>
    : T[P];
};

// Record creates an object type with specific keys and value type
type UserRole = 'admin' | 'editor' | 'viewer';

type RolePermissions = Record<UserRole, string[]>;
// { admin: string[]; editor: string[]; viewer: string[]; }

const permissions: RolePermissions = {
  admin: ['read', 'write', 'delete'],
  editor: ['read', 'write'],
  viewer: ['read'],
};

// Record with complex types
type HttpMethod = 'GET' | 'POST' | 'PUT' | 'DELETE';
type RouteHandler = (req: Request) => Response;

type RouteHandlers = Record<HttpMethod, RouteHandler>;