Typescript Map all enum values as key

Question

I declare a map so I can convert the numeric enum value into the value our API expects.

export const StatusMap: ReadonlyMap<Status, string> = new Map([
    [Status.NEW, 'new'],
    [Status.PENDING, 'pending'],
]);

But when I do statusMap.get(Status.NEW) it always tells me that the return value is possibly undefined. Is there a way to force a map (or similar) to contain all enum values?

And yes I know you can technically do

export enum Status {
    NEW = 'new',
    PENDING = 'pending',
}

but let's be honest, this kind of ruins the point of enums (IMO).

If you can use regular object instead of Map it will be as simple as Record<Status, string>. But what's the point of mapping strings to numbers and vice versa if the api expects the strings? String enum doesn't ruin the point of enums — Aleksey L.
– Aleksey L., Commented May 29, 2020 at 9:11
@AlekseyL. well, strings are way larger than numbers. It's not "enumerated" anymore. I could just do type Status = 'new' | 'pending'; — Elias
– Elias, Commented May 29, 2020 at 9:18
@AlekseyL. Problem is that I'm implementing a cache + a local store lol. So they're not just in the API but also caches separately. But I will definitely consider your argument. :) thanks — Elias
– Elias, Commented May 29, 2020 at 9:50
Anyway answering original question - you can define type StatusMap = { get<T extends Status>(status: T): string } and use it for statusMap. Pay attention, it won't verify that all enum values are actually in map typescriptlang.org/play/index.html#code/… — Aleksey L.
– Aleksey L., Commented May 29, 2020 at 11:45
And here's version with object as map (it will verify all the enum members are listed in map) typescriptlang.org/play/index.html#code/… — Aleksey L.
– Aleksey L., Commented May 29, 2020 at 11:48

Aleksey L. · Accepted Answer · 2020-05-30 04:00:44Z

17

If you can use regular object instead of Map, it can be defined as Record of enum members:

const statusMap: Record<Status, string> = {
    [Status.NEW]: 'new',
    [Status.PENDING]: 'pending',
};

Playground

Another option would be using type assertion that guarantees that all enum members are in the map:

type StatusMap = { get<T extends Status>(status: T): string }

const statusMap = new Map([
    [Status.NEW, 'new'],
    [Status.PENDING, 'pending'],
]) as StatusMap;

** Pay attention, with this approach it is not guaranteed that all the enum members are in the map at runtime, so if you choose to go this way - better to cover it by unit test.

answered May 30, 2020 at 4:00

Aleksey L.

38.4k11 gold badges86 silver badges90 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Joe Sadoski Over a year ago

In your first example, Record, is it appropriate/good form to get a value with statusMap[<one of Status>]? The reason I gravitated to a Map is to use .get().

Aleksey L. Over a year ago

@JoeSadoski could you elaborate on what's the issue with statusMap[Status.NEW]?

Joe Sadoski Over a year ago

Sorry, please disregard that. I misunderstood how Record worked. I thought they worked like objects, where you could use dot notation OR bracket notation. Your TS Playground example explained their use better for me. Thank you!

Collectives™ on Stack Overflow

Typescript Map all enum values as key

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related