CODEWITHSUNDEEP
typescript
ZiiMakc
ZiiMakc

Reputation: 37066

Generic optional type with extends for typecheck

Playground

I want to make api request like this:

// api Request
const body: ReqBody = { book: ['id', 'title'], author: ['name']}
const fn = async () => {
  const book: BookPropsOk = await fetch('api', {body: JSON.stringify(body)}) as any
}

Problem is idn how to make type with optional author if i will fetch only book fields?

// types
export type Book = {
  id: string
  title: string
}

export type Author = {
  id: string
  name: string
}

type BookFields = 'id' | 'title' 
type AuthorFields = 'id' | 'name' 

// generic response type from api (CHANGE THIS)
type ApiResBook<PickedBookFields extends BookFields, PickedAuthorFields extends AuthorFields> =
Pick<Book, PickedBookFields> & {
  author: Pick<Author, PickedAuthorFields>
}

type BookPropsOk = ApiResBook<'id' | 'title', 'name'>

type ReqBody = {
  book: BookFields[]
  author?: AuthorFields[]
}

// what if i want to fetch only book without author?
type BookPropsHowToMakeAuthorOptional = ApiResBook<'id' | 'title'>

Upvotes: 1

Views: 63

Answers (1)

ZiiMakc
ZiiMakc

Reputation: 37066

Hm, seems extends and pick works with never default:

type ApiResBook<PickedBookFields extends BookFields, PickedAuthorFields extends AuthorFields = never> =
Pick<Book, PickedBookFields> & {
  author: Pick<Author, PickedAuthorFields>
}

Upvotes: 1

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