Support typescript format configuration file

🚀 Feature Proposal

To be able to fully use TypeScript

Motivation

Make the .js file not appear in the project.

Example

This allows us to TypeScript ONLY.

Expected:

// File path: project/jest.config.ts
import { Configuration } from "jest";
import { defaults } from "jest-config";

const configure: Configuration = {
    preset: 'ts-jest',
    testEnvironment: 'jest-environment-jsdom-fourteen',
    globals: {
        'ts-jest': {
            isolatedModules: true,
        },
    },
    moduleFileExtensions: [...defaults.moduleFileExtensions, 'ts', 'tsx'],
}

export default configure

Pitch

Why does this feature belong in the Jest core platform?

Common feature proposals that do not typically make it to core:

• New matchers (see jest-extended)
• Changes to the default reporter (use custom reporters instead)
• Changes to node/jsdom test environments (use custom environments instead)

Reference

https://github.com/kulshekhar/ts-jest/issues/1415

[glennreyes]

I don’t think this is worth it. Jest runs on Node and requires your config file using Node. For jest to support .ts config files it would need to transpile it and then run it, which you could do yourself very easily if you really need a Typescript configuration file.

Although jest handles transpilation very well thanks to babel-jest and Babel, it does so in the tests once jest if fully configured, loaded and up and running. Having to do this transpilation just to read the configuration file can be both difficult or cumbersome to implement and result in a slower setup.

I just haven’t seen and can’t think of a project that needs a jest configuration so complex that type checking for it becomes necessary. Jest already supports complex scenarios like monorepos very well with relatively simple configurations. The fact that you use and like typescript doesn’t mean you have to use it in every single line of code and every file must be a .ts file.

I disagree. To me it’s a huge win if I can get a fully typed configuration without ever having to look up the documentation for every single option anymore. I’d rather have auto suggestions popping up in my editor than an X ms faster initial execution.

[Gamote]

@septs, @nvdnkpr, @G-Rath, @brieb, @dl748, @glennreyes

Hi guys, I hope this is what you were looking for: #10564 ✌️