编译时未定义 TypeScript 枚举

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

Answer 4

Similar issue here, but a slightly different cause & solution. Posting here in hopes that this helps others.

1. I was defining my enum in a file /auth/types.ts :

....
export enum SampleEnum {
    FIRST = 1,
    SECOND = 2
}

2. I was then exporting my types en-masse from /auth/index.ts :

export * from './types;

3. Finally, I was importing this from the parent directory elsewhere in the app:

import { SampleEnum } from './auth'
...

const someOtherObject = {
  place: SampleEnum.FIRST
}

Running Jest, I was getting the TypeError: Cannot read property 'FIRST' of undefined error, even when the code compiled just fine.

To solve this, I switched my import statement to

import { SampleEnum } from './auth/types'