Enum as Parameter in TypeScript

Question

Isn\'t it possible to set the type of a parameter to an Enum? Like this:

private getRandomElementOfEnum(e : enum):string{
    var length:number = Object.         


        

Answer 1

I agree with @Tarh. Enums in TypeScript are just Javascript objects without a common interface or prototype (and if they are const enum, then they are not even objects), so you cannot restrict types to "any enum".

The closest I could get is something like the following:

enum E1 {
    A, B, C
}
enum E2 {
    X, Y, Z
}

// make up your own interface to match TypeScript enums
// as closely as possible (not perfect, though)
interface Enum {
    [id: number]: string
}

function getRandomElementOfEnum(e: Enum): string {
   let length = Object.keys(e).length / 2;
   return e[Math.floor((Math.random() * length))];
}

This works for all enums (without custom initializers), but it would also accept other arrays as input (and then fail because the method body relies on the very specific key structure that TypeScript enums have).

So unless you have a real need for such a "generic" function, make typesafe functions for the individual enum types (or a union type like E1|E2|E3) that you actually need.

And if you do have this need (and this might very well be an X-Y-problem that can be solved in a better, completely different way given more context), use any, because you have left typesafe territory anyway.