Utility types

type User = { name: string; age: number };
type OptionalUser = Partial<User>;
 
const user: OptionalUser = { name: "Hamim" }; // ঠিক আছে, age না দিলেও চলবে

type User = { name?: string; age?: number };
type FullUser = Required<User>;
 
const user: FullUser = { name: "Hamim", age: 18 }; // সব দিতে হবে

type User = { name: string; age: number };
type ReadonlyUser = Readonly<User>;
 
const user: ReadonlyUser = { name: "Hamim", age: 20 };
// user.age = 25; ❌ Error — পরিবর্তন করা যাবে না

type Roles = "admin" | "user";
type AccessMap = Record<Roles, boolean>;
 
const access: AccessMap = {
  admin: true,
  user: false,
};

type User = { name: string; age: number; email: string };
type BasicInfo = Pick<User, "name" | "email">;
 
const user: BasicInfo = { name: "Hamim", email: "hamim@gmail.com" };

type User = { name: string; age: number; email: string };
type NoEmail = Omit<User, "email">;
 
const user: NoEmail = { name: "Hamim", age: 20 };

type Status = "loading" | "success" | "error";
type NoError = Exclude<Status, "error">; // "loading" | "success"

type A = "a" | "b" | "c";
type B = "b" | "c" | "d";
type Common = Extract<A, B>; // "b" | "c"

type Value = string | null | undefined;
type CleanValue = NonNullable<Value>; // string

function greet(name: string, age: number) {}
type Params = Parameters<typeof greet>; // [string, number]

function getAge(): number {
  return 25;
}
type Age = ReturnType<typeof getAge>; // number