[Typescript Challenges] 16. Medium - Omit

Implement the built-in Omit<T, K> generic without using it.

Constructs a type by picking all properties from T and then removing K

For example

interface Todo {
  title: string
  description: string
  completed: boolean
}

type TodoPreview = MyOmit<Todo, 'description' | 'title'>

const todo: TodoPreview = {
  completed: false,
}

 

Have to use remapping keywrod as, [P in keyof T as P extends K ? never: P], cannot just do [P in keyof T extends K...]

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#key-remapping-in-mapped-types

/* _____________ Your Code Here _____________ */

type MyOmit<T, K> = {
  [P in keyof T as P extends K ? never: P]: T[P]
}


/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'
type x = MyOmit<Todo, 'description'>
type cases = [
  Expect<Equal<Expected1, MyOmit<Todo, 'description'>>>,
  Expect<Equal<Expected2, MyOmit<Todo, 'description' | 'completed'>>>,
]

// @ts-expect-error
type error = MyOmit<Todo, 'description' | 'invalid'>

interface Todo {
  title: string
  description: string
  completed: boolean
}

interface Expected1 {
  title: string
  completed: boolean
}

interface Expected2 {
  title: string
}