Can I define a typescript variable that is an enum and a function?

Question

Here is the code so far:

function fr(this: any, value: number) {
  return Object.keys(this).find(k => this[k] === value);
}

type getEnumValue = (value: number) => string;
type myEnum = typeof enumVal;

enum enumVal {
  a = 1,
  b = 2
}

let EnumEval = fr.bind(enumVal) as getEnumValue | myEnum;
Object.assign(EnumEval, enumVal);

// Why are the casts required?
console.log((EnumEval as myEnum).a);
console.log((EnumEval as getEnumValue)(1));

console.log(EnumEval as myEnum.a);
console.log(EnumEval(1));

TS errors on the final two lines, requiring me to cast. Why?

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Can you tell me what is your motivation to use enum in such way? Enum should be used as enum, so just simple variant. — Maciej Sikora
– Maciej Sikora, Commented Jan 28, 2020 at 12:35
@MaciejSikora a non TS user was saying that TS couldn't handle this typing, and I was having trouble actually showing the user that it could. Since the primary purpose of this code is to be able to get a text value or int value from the same object I did let them know that Enums in TS already solve this for you in a way simpler way. — Daryl
– Daryl, Commented Feb 2, 2020 at 18:28

Aleksey L. · Accepted Answer · 2020-01-28 12:41:29Z

1

Here you go:

let EnumEval = fr.bind(enumVal) as (((value:number) => string) & (typeof enumVal));

Or:

let EnumEval = fr.bind(enumVal) as (typeof fr & typeof enumVal);

Variable that is an enum and a function - so it should be intersection (&), not a union (|)

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edited Jan 28, 2020 at 12:41

answered Jan 28, 2020 at 12:35

Aleksey L.

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