type UnionThing<T> = T | (value:T)=>T
I have union type like this : one generic primitive value and one function type
type FnThing<T> = ~~~~~ // expect it to be (value:T)=>T
Now I want to pick function type only but don't know how to.
Utility Type Pickis for key value and I don't have key in this union type.
How can I achieve this?
The problem here is that your expected type is not valid TypeScript.
This
type FnThing = (value: T) => T
would not compile since T is not declared anywhere. So we will have to either make FnThing generic over T or subsitute a type for T.
type FnThing<T> = Extract<UnionThing<T>, (args: any) => any>
type WithoutGeneric = FnThing<number>
// type WithoutGeneric = (value: number) => number
or
type FnThing2 = Extract<UnionThing<number>, (args: any) => any>
// type FnThing2 = (value: number) => number