Allow transparent loading of TypeScript custom reporters (by implementing requireAndTranspileModule in TestScheduler.ts loading custom reporters?)

[nelsonjchen]

I couldn't find an existing issue talking about this.

🚀 Feature Proposal

It would be great to be able to load TypeScript custom reporters directly.

I don't know if implementing this TODO allows for this:
https://github.com/facebook/jest/blob/3f107a33775cdff94cab6993741e3a1a22e00aa0/packages/jest-core/src/TestScheduler.ts#L329-L330

Jest 26 has already come, but this TODO wasn't fulfilled before 26.

Motivation

Implementing this into Jest would keep the overall project build config cleaner.

The alternative is to transpile the custom reporter manually from TS to JS or have to write the custom reporter in JS. These necessitate more build and IDE configuration. It's a similar motivation for plain TS files underneath __tests__ currently "just working".

Example

User writes a TypeScript custom reporter. And without compiling the TS, they can specify the TS script directly as a custom reporter.

It would look something like this in the config.

{
  "reporters": ["default", "<rootDir>/my-custom-reporter.ts"]
}

Pitch

There may be a chicken and egg problem with a Typescript config, but there shouldn't be one for reporters. We can currently load Typescript tests without compiling so why not TS reporters?

[jeysal]

Thanks. I've amended the umbrella issue for transforming things from the config to also include this - cleaner to have it all there :)

[aslettemark]

Is there a known "best way" to work around this for the time being?

[Bnaya]

@aslettemark what i did:
You create intermediate js file that uses ts-node/babel-node register and requiring the actual file

// reporter.js

// jest can't transpile transformers on the fly so we help him
// https://github.com/facebook/jest/issues/10105

/* eslint-disable import/no-extraneous-dependencies */
const tsNode = require('ts-node');

tsNode.register({
    transpileOnly: true,
    compilerOptions: require('@testim/root-cause-jest/tsconfig').compilerOptions,
});

const Reporter = require('@testim/root-cause-jest/lib/reporter/default');

module.exports = Reporter;

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