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Henok Tesfaye
Henok Tesfaye

Reputation: 9560

Using an enum inside enum in typescript?

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?

Upvotes: 8

Views: 8731

Answers (1)

georg
georg

Reputation: 214959

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); // compiles
func('foo', 'bar', 99); // compiles 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); // compiles
define('foo', 'bar', 99); // doesn't compile

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

Upvotes: 4

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