javascript - Using an enum inside enum in typescript? - Stack Overflow

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enum KINDS {
  STATIC = 1,
  FIELD,
  ARG,
  VAR
}

enum ALL_KINDS {
  STATIC = 1,
  FIELD,
  ARG,
  VAR,
  NONE
}

How can I reuse the first enum inside the second one?

enum KINDS {
  STATIC = 1,
  FIELD,
  ARG,
  VAR
}

enum ALL_KINDS {
  STATIC = 1,
  FIELD,
  ARG,
  VAR,
  NONE
}

How can I reuse the first enum inside the second one?

• javascript
• typescript
• enums

Share Improve this question Follow asked Sep 29, 2019 at 19:07 Henok TesfayeHenok Tesfaye 9,6201515 gold badges5151 silver badges9292 bronze badges 2

• By "re-use" you mean you want ALL_KINDS to include the entries, with the same values, from KINDS? – Dave Newton Commented Sep 29, 2019 at 19:13
• Yup @DaveNewton. – Henok Tesfaye Commented Sep 29, 2019 at 20:07

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1 Answer 1

Sorted by: Reset to default 4

AFAIK, extending enums is under consideration, in the meantime you can use const objects instead:

const KINDS = <const>{
  STATIC: 1,
  FIELD: 2,
  ARG: 3,
  VAR: 4
};

const ALL_KINDS = <const>{ ...KINDS, NONE: 5 };

There are also other workarounds in the above thread.

If you want this type to be checked, note that from the type perspective, a numeric enum is equivalent to number:

enum KINDS {
  STATIC,
  FIELD,
  ARG,
  VAR
}

declare function func(name: string, type: string, kind: KINDS): any;

func('foo', 'bar', KINDS.ARG); // piles
func('foo', 'bar', 99); // piles too (?)

If you use an object as suggested above, you can also enforce strict type checking by creating a type for all possible values of that object:

const KINDS = <const>{
  STATIC: 1,
  FIELD: 2,
  ARG: 3,
  VAR: 4
};

type KIND_VALUE = typeof KINDS[keyof typeof KINDS]

declare function define(name: string, type: string, kind: KIND_VALUE): any;

define('foo', 'bar', KINDS.ARG); // piles
define('foo', 'bar', 99); // doesn't pile

This is a bit more verbose, but then you have your type actually checked.

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