Readonly, Exclude, Extract, NonNullable

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Readonly<T>

interface Config { host: string; port: number; }
const cfg: Readonly<Config> = { host: 'localhost', port: 3000 };
// cfg.host = 'remote'; // Error!

Exclude<T, U>

type Status = 'pending' | 'active' | 'banned' | 'deleted';
type ActiveStatus = Exclude<Status, 'banned' | 'deleted'>;
// 'pending' | 'active'

Extract<T, U>

type StringOrNumber = string | number | boolean;
type JustStrNum = Extract<StringOrNumber, string | number>;
// string | number

NonNullable<T>

type MaybeString = string | null | undefined;
type DefinitelyString = NonNullable<MaybeString>; // string

ReturnType<T>

function fetchUser() { return { id: 1, name: 'Alice' }; }
type User = ReturnType<typeof fetchUser>; // { id: number; name: string }

Parameters<T>

function add(a: number, b: number): number { return a + b; }
type AddParams = Parameters<typeof add>; // [number, number]

InstanceType<T>

class HttpClient { get(url: string) { return fetch(url); } }
type Client = InstanceType<typeof HttpClient>; // HttpClient

Awaited<T>

type A = Awaited<Promise<string>>;          // string
type B = Awaited<Promise<Promise<number>>>;  // number

Menggunakan Beberapa Utilitas Bersama

type SafeInput<T> = Readonly<Partial<NonNullable<T>>>;

Tipe Utilitas Hanyalah Alias Tipe

Pemeriksaan Singkat

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