Unable to perform a union operation that combines multiple enums into one

Here is a basic example:

export enum EnumA {
  A = 'a',
}

export enum EnumB {
  A = 'b',
}

export class SomeEntity {
  id: string;

  type: EnumA | EnumB;
}

const foo = (seArray: SomeEntity[]) => {
  seArray.forEach((se) => {
    Object.values(EnumA).includes(se.type)
  })
}

However, an error is encountered:

TS2345: Argument of type 'EnumA | EnumB' is not assignable to parameter of type 'EnumA'.   Type 'EnumB' is not assignable to type 'EnumA'.

Upon reviewing the ts docs, it is unclear why this error is occurring as se.type should be one of the values from the union of enums. Could there be some nuances about enums that I am overlooking?

Answer №1

The issue arises because Typescript is unaware of your intention for Object.values(EnumA) to represent an array containing instances of both EnumA and EnumB; instead, it assumes that you want it to be an array solely composed of EnumAs. This leads to the error message pointing out that se.type is not present. To resolve this, you can explicitly define a broader type for Object.values(EnumA), like so:

const foo = (seArray: SomeEntity[]) => {
  seArray.forEach((se) => {
    const values: (EnumA | EnumB)[]  = Object.values(EnumA);
    values.includes(se.type);
  })
}

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