TypeScript: Enum.Value is not comparable to some other Enum.Value

Question

I have placed an enum in a seperate file so I can use that enum across files

Enums.ts

export enum Category {
    NotDefined,        
    BackData,
    Testing,
    Simulated
}

In another file i try to use my enum. I am trying to write a simple if/else or switch.

If i set the value of category == Category.Testing vscode is happy. If i try to set the value to something else e.g. "backData" as in the example below I get an error:

Type 'Category.Testing' is not comparable to type 'Category.BackData'

Example code:

import { Category } from '@app/model/Enums.ts';

public async SubmitForm(): Promise<Boolean> {
    var category: Category;
    category = Category.BackData;

    switch (category) {
      case (Category.Testing): {
        ...
      }
      default: {
        ...
      }
    }

    if (category == Category.Testing) {
      ...
    } else {
      ...
    }
}

The error when setting the enum to another value that testing

Possible duplicate of Why does a switch statement on an enum throw 'not comparable to type' error? — Christopher Peisert
– Christopher Peisert, Commented Aug 19, 2019 at 1:27
It is the same question, but the answer i received if different that the answers suggest in that question. I will therefore choose not to mark it a duplicate. — Tony
– Tony, Commented Aug 19, 2019 at 2:06

Shalom Peles · Accepted Answer · 2019-08-19 01:25:16Z

1

As a workaround (for testing purposes only) you can write:

category = Category.BackData as Category;

answered Aug 19, 2019 at 1:25

Shalom Peles

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Shanon Jackson · Accepted Answer · 2019-08-19 03:17:00Z

0

Typescript enums are nominal or opaque meaning that they are globally unique and unassignable to other or other types even if they're both the same.

export type IsEqual<A, B> = [A] extends [B] ? [B] extends [A] ? true : false : false

enum Foo {
    Foo
}

enum Bar {
    Bar
}

enum FooStr {
    Foo  = "hello"
}

enum BarStr {
    Bar = "hello"
}

type WhatType = IsEqual<Foo, Bar> // false.
type WhatType1 = IsEqual<Foo.Foo, Bar.Bar> // false even though both are 0
type WhatType2 = IsEqual<FooStr.Foo, BarStr.Bar> // false even though both are "hello"

answered Aug 19, 2019 at 3:17

Shanon Jackson

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