utility-types

import { DeepReadonly, Optional, Falsy, Primitive, Nullish } from 'utility-types'; interface User { id: number; name: string; email?: string; settings: { theme: 'dark' | 'light'; notificationsEnabled: boolean; }; } // DeepReadonly: Makes all properties, including nested ones, readonly. type ImmutableUser = DeepReadonly<User>; const user: ImmutableUser = { id: 1, name: 'Alice', settings: { theme: 'dark', notificationsEnabled: true, }, }; // user.name = 'Bob'; // Error: Cannot assign to 'name' because it is a read-only property. // user.settings.theme = 'light'; // Error: Cannot assign to 'theme' because it is a read-only property. // Optional<T, K>: Makes specific keys K in T optional. type UserWithOptionalId = Optional<User, 'id'>; const newUser: UserWithOptionalId = { name: 'Bob', settings: { theme: 'light', notificationsEnabled: false }, }; // Falsy: Represents common "falsy" values in JavaScript. function isFalsyValue(value: unknown): value is Falsy { return !value; // A simple runtime check for demonstration } console.log(`Is 0 falsy? ${isFalsyValue(0)}`); // true console.log(`Is 'hello' falsy? ${isFalsyValue('hello')}`); // false // Primitive: Represents non-object types. type MyPrimitive = Primitive; let p: MyPrimitive = 123; p = 'hello'; p = true; // p = { a: 1 }; // Error: Type '{ a: number; }' is not assignable to type 'Primitive'. // Nullish: Represents null or undefined. type MaybeString = string | Nullish; const s1: MaybeString = "hello"; const s2: MaybeString = null; const s3: MaybeString = undefined; // const s4: MaybeString = false; // Error: Type 'false' is not assignable to type 'string | null | undefined'. // This quickstart demonstrates how to use several key utility types from the `utility-types` // library, including `DeepReadonly` for deep immutability, `Optional` for making specific // properties optional, and `Falsy`, `Primitive`, and `Nullish` for working with common // JavaScript value classifications at the type level.