Loading .cjs config files on Node 13

🚀 Feature Proposal

If you have Node 13 and jest.config.js file in a package with type=module then Node will emit a warning:

(node:8906) Warning: require() of ES modules is not supported.
require() of /home/spyke/Projects/undercut/packages/undercut/jest.config.js from /home/spyke/Projects/undercut/node_modules/jest-config/build/readConfigFileAndSetRootDir.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
Instead rename jest.config.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from /home/spyke/Projects/undercut/packages/undercut/package.json.

In case of manually specifying the config fole with --config jest.config.cjs it fails with an error:

The --config option requires a JSON string literal, or a file path with a .js or .json extension.
Example usage: jest --config ./jest.config.js

Using ES Modules syntax for config file gives an error too:

SyntaxError: Unexpected token 'export'

The issue is the same as babel/babel#10595. .cjs is mandatory, but being able to load an ESM from .js or .mjs is nice to have too.

Motivation

Support ES Modules workflows in Node13+

Example

Configuring Jest in packages with type=module and config file named jest.config.cjs

Pitch

[kirill-konshin]

The problem is that after upgrade of Node from 12.15 to 12.16 warning become an error.

I have a type=module, jest.config.js and .babelrc.js in my setup, it worked with warning, now it does not. Just putting a reference here for anyone who’ll look for more info just in case.

So in essence this ticket also applies to Node 12, not just 13 as mentioned in title.

[emma-borhanian]

@SimenB Yup, jest 25.

Maybe you missed a spot? https://github.com/facebook/jest/blob/v25.1.0/packages/jest-cli/src/cli/args.ts#L55

  if (
    argv.config &&
    !isJSONString(argv.config) &&
    !argv.config.match(/\.js(on)?$/)
  ) {
    throw new Error(
      'The --config option requires a JSON string literal, or a file path with a .js or .json extension.\n' +
        'Example usage: jest --config ./jest.config.js',
    );
  }

undercut test log: https://gist.github.com/emma-borhanian/94a233217b2f8551157291aa3adcc956