CODEWITHSUNDEEP
typescript
SlothFriend
SlothFriend

Reputation: 641

How can I use a generic interface to enhance an existing interface with additional value types?

I'd like to build a generic interface so that it can extend the allowed value types of a given interface. I try to illustrate this below....

If I have an interface as below...

interface Original {
  prop1: string
  prop2: number
}

How can I build a generic interface, let's say ExtraValueTypes<T> so that the result is as below?

type ExtraType = myType

interface WithExtraValueTypes {
  prop1: string | myType
  prop2: number | myType
}

such that...

ExtraValueTypes<Original> = WithExtraValueTypes

Upvotes: 1

Views: 33

Answers (1)

Eldar
Eldar

Reputation: 10790

You can make use of mapped types as below. All you need to a map definition that unions all the properties with Extra type.

interface Original {
  prop1: string
  prop2: number
}

type Extra = { a: string }

type Extrator<T> ={
    [P in keyof T] : T[P] | Extra
}

type ExtraOriginal = Extrator<Original>;

const sample: ExtraOriginal ={
    prop1: { a: "foo" },
    prop2 :3
}

const sample2: ExtraOriginal ={
    prop1: "foo",
    prop2 :{a:"bar"}
}

Playground

Upvotes: 3

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