Using Ramda with Typescript, passing down the types

Question

I have this small function, firstOrNull:

import { propOr } from 'ramda'

export const firstOrNull = propOr(null, '0')

And I want to use with a property that returns QueryDocumentSnapshot<DocumentData>[]

const organization = firstOrNull(snapshot.docs)?.data() as Organization

Because the lack of typing on firstOrNull, I got the error:

Object is of type 'unknown'

What I need to do to use the correct typing on firstOrNull?

May be change to something like that:

export const firstOrNull:<T[]> = propOr<null, T, number>(null, 0)

Answer 1

Add explicit type to firstOrNull that depends on the array it receives, so it can infer the correct type:

export const firstOrNull: <T>(arr: T[]) => T | null = propOr(null, '0')