TypeScript: Remap values in object while keeping type information

Question

Is it possible in TypeScript to map an objects values to another type that uses the actual type of the entry in the result?

Not sure how to describe it exactly, but here is what I'm trying to achieve:

const obj = {
    a: 1,
    b: true,
    c: "foo"
}

const result = toFunctions(obj)

// Type of result would be:
{
    a: (input: number) => any // because a was of type number
    b: (input: boolean) => any // because b was of type boolean
    c: (input: string) => any // because c was of type string
}

I'm trying to "reuse" the types from the source objects keys in the returned objects keys while performing some sort of transformation. In my case I want to wrap it in a function, but such a mechanism could possibly also return other aggregate types such as number[] or string[].

I'd like to do this in a generic way so that I can generate function types based on the keys of any object.

hackape · Accepted Answer · 2020-05-04 13:04:34Z

3

Mapped type is what you’re looking for.

type MapToFuncs<T> = {
  [K in keyof T]: (arg: T[K]) => any
}

function toFunctions<T>(source: T): MapToFuncs<T> { … }

answered May 4, 2020 at 13:04

hackape

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1 Comment

Thomas Over a year ago

Perfect. This seems to be exactly what I need!

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