Typescript: Is it possible to type an array to include every key of an enum

Question

Is it possible to type the enum array in a way that forces it to contain every single value of the EPostFromField enum?

This is a mongodb schema, and the use case would be to future proof the enum field if more enums are added later on (ie: have the compiler throw an error because the array doesn't have all the enum values enumerated).

As a bonus I guess the next level would be a solution that also guarantees that the enum array values are unique :)

export const enum EPostFromField {
  Resident = 'resident',
  AdminUser = 'admin-user', // Admin <user name>
  BoardUser = 'board-user', // Board <user name>
  AdminSociety = 'admin-society', // Admin <community name>
  BoardSociety = 'board-society', // Board <community name>
}

showPostAs: {
    type: String,
    default: EPostFromField.Resident,
    enum: [
      EPostFromField.Resident,
      EPostFromField.AdminUser,
      EPostFromField.BoardUser,
      EPostFromField.AdminSociety,
      EPostFromField.BoardSociety,
    ] as EPostFromField[], // DEVNOTE: Improve typing to enforce *every* unique key of enum
  },

Possible duplicate of [Enforce that an array is exhaustive over a union type](https://stackoverflow.com/questions/55265679/enforce-that-an-array-is-exhaustive-over-a-union-type) — jcalz, Jun 03 '20 at 00:28
enum objects, like all objects, have *keys* and *values* which are different. `"Resident"` is a *key*, but `EPostFromFileld.Resident` is its *value*. You talk about wanting to guarantee unique *keys*, but you are making an array of *values*. Are you using the word "key" when you mean "value"? If not, I'm confused; could you elaborate? — jcalz, Jun 03 '20 at 00:31
@jcalz Yes. Sorry for mixup. The end goal is to have the mongodb enum field contain (and therefore only accept) values of enum EPostFromField. Thank you and I will edit the question. — Bryan Oliveira, Jun 03 '20 at 15:41

Ben Smith · Accepted Answer · 2020-06-09T22:16:00.897

4

You could define a string enum and do the following:

enum EPostFromField {
    Resident = "Resident",
    AdminUser = "AdminUser",
    BoardUser = "BoardUser",
    AdminSociety = "AdminSociety",
    BoardSociety = "BoardSociety"
}

const epostFromFieldKeys = Object.keys(EPostFromField);

const epostFromFields = epostFromFieldKeys as EPostFromField[]

You can see this running in this playground link.

The values in the array would be unique if you define the string values in the enum uniquely(!).

edited Jun 09 '20 at 22:16

answered Jun 03 '20 at 00:11

Ben Smith

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Thanks Ben! Yes, in effect this answers my question :) I was however searching for something a bit more condensed. Take the typescript `Partial` utility type, I was hoping for something more along these lines (but instead of a partial match, a complete + mandatory + unique match). – Bryan Oliveira Jun 08 '20 at 16:46

Typescript: Is it possible to type an array to include every key of an enum

1 Answers1