Document the "official" type for what should be exported from jest.config.js

[G-Rath]

🚀 Feature Proposal

I feel a bit foolish asking this as in theory it should be somewhat obvious & easy...., but I can't figure out what type to use for the export of jest.config.js for TypeScript(-in-js) 😬

i.e with .eslintrc.js I can do:

/** @type {import('eslint').Linter.Config} */
const config = {
  ...
}

module.exports = config;

But for Jest theres a couple of different interfaces, each with their pros and cons: there's Project & Global, some with required properties, and others all optional, and then theres the normalised values...

I think it would be good to mark a type/interface as The Public Configuration Type, and put a line on the Configuring Jest page.

Motivation

This would let us be nice and type safe when configuring jest :D
It would also mean we'd not be having to use external schemas that need to be updated by third-parties.

Example

/** @type {import('jest-package').Config} */
const config = {
  ...
}

module.exports = config;

Pitch

Because it's already in the core... somewhere... 🕵

[SimenB]

In theory it's import('@jest/types').Config.InitialOptions. I don't know how well it works out in practice to use it though, it's designed for internal usage

[G-Rath]

@SimenB that seems to work pretty well.

One thing of note: ConfigGlobals is defined as a type of Record<string, any>, which means we can't use declaration merging to supplement it.

i.e ts-jest could merged its config into globals if ConfigGlobals was an interface, like so:

// ts-jest/index.d.ts
declare module '@jest/types' {
  namespace Config {
    interface ConfigGlobals {
      'ts-jest': TsJestGlobalOptions;
    }
  }
}

// jest.config.js
/** @type {import('@jest/types').Config.InitialOptions} */
const config= {
  globals: {
    'ts-jest': {
      isolatedModules: true,
      myProperty: 1 // error, "myProperty" is not defined!
    }
  }
}

module.exports = config;

Would it be alright if I opened a PR changing this?

[SimenB]

Yeah, sure 👍

[SimenB]

@G-Rath close this?

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.