feat(jest, jest-config): add defineConfig() helper

[mrazauskas]

Summary

Idea borrowed from Vue ecosystem (at this is there I saw it): a defineConfig() helper function which helps with types and autocompletion in CJS, ESM or TS:

It takes an object, or function, or async function:

// cjs
const {defineConfig} = require('jest');

module.exports = defineConfig({
  verbose: true,
});

// esm
import jest from 'jest';

export default jest.defineConfig(() => ({
  verbose: true,
}));

// ts
import {JestConfig, defineConfig} from 'jest';

export default defineConfig(async () => {
  const verbose: JestConfig['verbose'] = await asyncGetVerbose();

  return {verbose};
});

Is this interesting and useful? Or sort of exotic and complicated?

Test plan

E2e and type tests added.

[mrazauskas]

Still thinking. Perhaps it would be better to expose defineJestConfig(), JestConfig and jestDefaults from 'jest'? Or better from 'jest-config'? It is nice to install only jest, in the other hand these are just devDependencies.

[Smrtnyk]

this allows to have typed config without having @types/jest installed?

[mrazauskas]

this allows to have typed config without having @types/jest installed?

Hm.. Do you mean @jest/types? Somehow I was sure that @types/jest doesn't include types for config.

[mrazauskas]

Can’t figure out why, but import {defineConfig} from 'jest' throws an error in ESM. import {defineConfig} from 'jest-config' works as expected. Seems like they both export defineConfig in the same way. Strange.

[mrazauskas]

@SimenB @Smrtnyk What do you think?

Somewhat cleaner way to have type definitions and autocompletion in config files. The difference I am trying to introduce here is the following –

Current (JS with type hints and autocompletion, no type checks yet, but @jest/schema will do validation some day):

// jest.config.js

/** @type {import('@jest/types').Config.InitialOptions} */
const config = {
  verbose: true,
};

module.exports = config;

This branch:

const {defineConfig} = require('jest');

module.exports = defineConfig({
  verbose: true,
});

Current (TS with type checking through ts-node):

// jest.config.ts

import type {Config} from '@jest/types';

const config: Config.InitialOptions = {
  verbose: true,
};

export default config;

This branch (type checks still through ts-node):

import {defineConfig} from 'jest';

export default defineConfig({
  verbose: true,
});

[github-actions]

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