babel-jest createTransformer removed from Typescript?

[broksonic21]

🐛 Bug Report

In babel-jest 26.6.3, the index.d.ts is this (containing createTransformer):

import { TransformOptions } from '@babel/core';
import type { Transformer } from '@jest/transform';
interface BabelJestTransformer extends Transformer {
    canInstrument: true;
}
declare const transformer: BabelJestTransformer & {
    createTransformer: (options?: TransformOptions) => BabelJestTransformer;
};
export = transformer;

But in 27.0.1

it is

import { TransformOptions } from '@babel/core';
import type { SyncTransformer } from '@jest/transform';
declare const transformer: SyncTransformer<TransformOptions>;
export default transformer;

so createTransformer is no longer exposed. That usage is documented on lots of sites as the way to use babel-jest - i.e. https://babeljs.io/docs/en/config-files for example, which has you call like this, which no longer works:

module.exports = require("babel-jest").createTransformer({
  rootMode: "upward",
});

Is this intentional to change the typescript to drop createTransformer? If so, can the doc be updated, and what's the alternative?

To Reproduce

Steps to reproduce the behavior:

• Have babel-jest 26.6.3
• Upgrade it to 27.0.1 (in my case, I also was updating Jest for the same versions too)

Expected behavior

• Either typescript still exposes createTransformer
• or doc is updated with new steps

envinfo

26.6.3:

  System:
    OS: macOS 11.3.1
    CPU: (8) x64 Intel(R) Core(TM) i7-8569U CPU @ 2.80GHz
  Binaries:
    Node: 15.12.0 - /usr/local/bin/node
    npm: 7.6.0 - /usr/local/bin/npm
  npmPackages:
    jest: ^26.6.3 => 26.6.3

27.0.1:

  System:
    OS: macOS 11.3.1
    CPU: (8) x64 Intel(R) Core(TM) i7-8569U CPU @ 2.80GHz
  Binaries:
    Node: 15.12.0 - /usr/local/bin/node
    npm: 7.6.0 - /usr/local/bin/npm
  npmPackages:
    jest: ^27.0.1 => 27.0.1

[sibelius]

I can confirm that createTransformer is not working anymore for us

TypeError: createTransformer is not a function
packages/main/test/babel-transformer.js

[sibelius]

I think you need to do like this

const { configWeb } = require('babelconfig.js');

const transformer = require('babel-jest');

module.exports = transformer.createTransformer({
  ...configWeb,
});

[sibelius]

this does not work as well

[SimenB]

using require requires (hah) you to do require('babel-jest').default.createTransformer. Somewhat cleaner with fake ESM (like TypeScript or Babel), but unfortunately just as ugly with real ESM (double default) 😞 We'll probably migrate to emit proper ESM this summer when we drop node 10.

We might wanna export createTransformer in addition to sticking it on the default export? I didn't do it since Jest itself picks up createTransformer calls and calls it, but only on default - not as a named export.

@thymikee @jeysal thoughts?

[sibelius]

require('babel-jest').default.createTransformer is also breaking for us

[SimenB]

really? that works fine for me.

$ node -p "require('babel-jest').default.createTransformer"
[Function: createTransformer]

[broksonic21]

once resolved, can the docs be updated ASAP with the supported solution? https://babeljs.io/docs/en/config-files

[SimenB]

Babel docs are not kept in this repo

[SimenB]

(/cc @nicolo-ribaudo FYI)

[sibelius]

it is working now, maybe it was can cache issue

[broksonic21]

the .default also worked for me.

[nwalters512]

@SimenB although require('babel-jest').default.createTransformer works at runtime, as @broksonic21 pointed out in the original issue message, attempting to access createTransformer in a TypeScript file breaks because the type for the default export no longer reflects the existence of a createTransformer function:

import { TransformOptions } from '@babel/core';
-import type { Transformer } from '@jest/transform';
-interface BabelJestTransformer extends Transformer {
-    canInstrument: true;
-}
-declare const transformer: BabelJestTransformer & {
-    createTransformer: (options?: TransformOptions) => BabelJestTransformer;
-};
-export = transformer;
+import type { SyncTransformer } from '@jest/transform';
+declare const transformer: SyncTransformer<TransformOptions>;
+export default transformer;

I believe your suggestion to "export createTransformer in addition to sticking it on the default export" would resolve this; I'd be happy to open a PR with this change.

[dcwarwick]

Just to note that we've also hit this issue, but not using the typescript at all: just a regular JS transform using the conventional pattern as currently given in the docs.

Incidentally, here's a link to the docs in question, which give code that no longer works:
https://babeljs.io/docs/en/config-files#jest

Note: code something like the following provides a workaround which runs both on previous and newer versions, in case that's needed by anyone:

const babelJestMd = require('babel-jest');
const babelJest = babelJestMd.__esModule ? babelJestMd.default : babelJestMd;

module.exports = babelJest.createTransformer({
  // babel options
});

I note that Jest itself uses jest-utils interopRequireDefault to ensure everything it loads has a default field whichever pattern it was using.

[nwalters512]

I opened a PR to add a named export for createTransformer: #12399.

[SimenB]

https://github.com/facebook/jest/releases/tag/v28.0.0-alpha.1