Undefined TypeScript enum at compile time

Question

I have an enum defined in types.ts:

export enum Handedness {
  Left,
  Right,
  Both,
}

export type State = {
  count: number
  handedness: Handedness
}

and I have an object being initialized in state.ts:

import { State, Handedness } from './types'

export const initial: State = {
  count: 0,
  handedness: Handedness.Both
}

When I run tests (via jest) for this project, state.ts generates an error TypeError: Cannot read property 'Both' of undefined, telling me that Handedness isn't defined at the time it's referenced. But I'm exporting it from its module and importing it before I use it... so it should be defined.

I've found other similar questions asking about undefined enums, but they seem to all be asking about runtime. This is a compile time problem as far as I can tell.

I don't see what I would be doing wrong here. I import other types in other places without issue. But this enum simply doesn't want to work. What is going on here and how can I work around it?

Answer 1

Well, this isn't a way to get this to work, but this GitHub PR explains that ts-jest won't support enums that work like this. I've changed all uses to (e.g.) ("both" as Handedness) and it works. So, that's not an explanation, it's a workaround.

Answer 2

You can also try using const enums.

So change:

export enum Whatever { ... }

to

export const enum Whatever { ... }

Apparently as of ts-jest version 23.10 you can just do this. Much better!

Answer 3

I encountered similar error while running my code with Jest. The issue was caused by a React component that imported an enum type from a module which was also being mocked with jest.mock. I fixed the issue by using jest.spyOn for method that I needed instead of whole module.

from: jest.mock("example/path", () => ({ useExampleMethod: () => {...

to: import * as exampleModule from "example/path"; jest.spyOn(exampleModule , 'useExampleMethod').mockReturnValue({...