type ClassPublicKeys<T> = keyof T; 

Solution by so11y #27224

2828 - ClassPublicKeys

I am shocked to my core that this challenge is in the "hard" difficulty set. It should literally be in the "easy" difficulty set. Oh well. I think this is the shortest answer to any of the type challenges (literally). Prepare for a laugh on this one.

🎥 Video Explanation

🔢 Code

// ============= Test Cases =============
import type { Equal, Expect } from './test-utils'

class A {
  public str: string
  protected num: number
  private bool: boolean
  constructor() {
    this.str = 'naive'
    this.num = 19260917
    this.bool = true
  }

  getNum() {
    return Math.random()
  }
}

type A1 = ClassPublicKeys<A>;
type B1 = 'str' | 'getNum';
type C1 = Expect<Equal<A1, B1>>;

// ============= Your Code Here =============
// @zhaoyao91 explanation:
//
// In TypeScript, when you wrote a class A,
// you defined two types in its type system:
//
//  1. `A` is the type of the instance of class `A`
//
//  2. `typeof A` is the type of the class object
//       say `class A`
//
// So, any instance of class A is just an object,
// keyof keyword return its public fields.

type ClassPublicKeys<T> = keyof T;

// ============== Alternatives ==============
type ClassPublicKeys<T, P = keyof T> =
  P extends keyof T
  ? P
  : never;

➕ More Solutions

For more video solutions to other challenges: see the umbrella list! https://github.com/type-challenges/type-challenges/issues/21338

Solution by dimitropoulos #25353

type ClassPublicKeys<T> = keyof T;

Solution by E-uler #24973

type ClassPublicKeys<T> = keyof T

Solution by NeylonR #24598

// your answers
type ClassPublicKeys<T> = keyof T

Solution by jxhhdx #24337

// your answers
type ClassPublicKeys<A> = keyof A

Solution by snakeUni #23919

type ClassPublicKeys<A> = keyof A

In typescript, when you wrote a class A, you defined two types in its type system:

• A is the type of the instance of class A
• typeof A is the type of the class object, sayclass A

So, any instance of class A is just an object, keyof keyword return its public fields.

Solution by zhaoyao91 #21570

// your answers
//this is i have resolve question that the easiest and the the most ingenious   
type ClassPublicKeys<T> = keyof T

Solution by YqxLzx #21448

type ClassPublicKeys<T> = keyof T

Solution by so11y #21250

// your answers
type publicKyes1<A1, k = keyof A1> = k extends keyof A1 ? k : never; 

Solution by fengjinlong #20297

type ClassPublicKeys<T> = keyof T;

Solution by CaoXueLiang #19471

// your answers
type ClassPublicKeys<T> = keyof T;

Solution by jiaaoMario #17753

type UnionToFunc = T extends unknown ? (arg: T) => void : never; type UnionToIntersection = UnionToFunc extends (arg: infer Arg) => void ? Arg : never; type LastInUnion = UnionToIntersection<UnionToFunc> extends (x: infer L) => void ? L : never; type UnionToTuple<T, L = LastInUnion> = [L] extends [never] ? [] : [...UnionToTuple<Exclude<T, L>>, L]; type TupleToUnion<T extends any[]> = T extends [infer el, ...infer rest] ? el | TupleToUnion : never;

type ClassPublicKeys = TupleToUnion<UnionToTuple>;

Solution by my5201314zwl #16697

// your answers

type ClassPublicKeys<T> = keyof T

// your answers
type ClassPublicKeys<T> = keyof T ;

type ClassPublicKeys<T extends any> = keyof T;

// your answers
type ClassPublicKeys<A> = keyof A

type ClassPublicKeys<TClass> = keyof TClass

// your answers
type ClassPublicKeys<T> = keyof T;

type ClassPublicKeys<T> = keyof T

type ClassPublicKeys<T extends Record<string, any>, K extends keyof T = keyof T> = K

class A {
  public str: string
  protected num: number
  private bool: boolean
  constructor() {
    this.str = 'naive'
    this.num = 19260917
    this.bool = true
  }

  getNum() {
    return Math.random()
  }
}

// public 
type testPublic = 'str' extends keyof A ? true : false

// protected
type testProtected = 'num' extends keyof A ? true : false

// private 
type testPrivate = 'bool' extends keyof A ? true : false

type testClass = ClassPublicKeys<A>

class A {
  public str: string
  public greetings: string
  protected num: number
  private bool: boolean
  constructor() {
    this.str = 'naive'
    this.greetings = 'hello'
    this.num = 19260917
    this.bool = true
  }

  getNum() {
    return Math.random()
  }
}

type ClassPublicKeys<T, K = keyof T> = K extends keyof T
  ? K
  : never

type cases = [Expect<Equal<ClassPublicKeys<A>, 'str' | 'greetings' | 'getNum'>>]

type ClassPublicKeys<T, K = keyof T> = K extends keyof T ? K : never

type ClassPublicKeys<A> = keyof A; // 😄

type ClassPublicKeys<A> = keyof A

type ClassPublicKeys<T extends any,K = keyof T> = K extends keyof T? T extends Pick<T,K>?K:never : never;

// :D
type ClassPublicKeys<A> = keyof A