Type Aliases in TypeScript

// Object type
type User = {
  id: number;
  name: string;
  email: string;
};

// Primitive alias
type UserId = string;
type Age = number;

// Union type
type Status = "active" | "inactive" | "pending";

// Function type
type Callback = (error: Error | null, result?: unknown) => void;

// Tuple type
type Pair = [string, number];

// Union types (not possible with interfaces)
type Result<T> = { success: true; data: T } | { success: false; error: string };

// Mapped types
type Readonly<T> = { readonly [K in keyof T]: T[K] };

// Conditional types
type IsString<T> = T extends string ? true : false;

// Template literal types
type EventName = `on${Capitalize<string>}`;

// API response with discriminated union
type ApiResponse<T> = {
  success: true;
  data: T;
  pagination?: { page: number; total: number };
} | {
  success: false;
  error: { code: string; message: string };
};

// Utility types
type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends object ? DeepPartial<T[P]> : T[P];
};