"Cannot read property 'length' of undefined" in Jest 27

Question

"Cannot read property 'length' of undefined" in Jest 27

Closed this issue 3 years ago · 8 comments

After upgrading to jest@27 and babel-jest@27 I'm now getting the following errors with this transformer:

    TypeError: Cannot read property 'length' of undefined

      at Object.createTransformer [as process] (node_modules/jest-transformer-mdx/index.js:22:42)
      at ScriptTransformer.transformSource (node_modules/@jest/transform/build/ScriptTransformer.js:612:31)
      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:758:40)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:815:19)
      at Object.<anonymous> (pages/chrome/index.tsx:6:1)

Answer 1 · 2021-05-26T16:27:25.000Z

Okay this library was last tested with jest 24 (and the last update was when jest 26 was the latest version, so it seems jest 26 could also be the last stable version). What does your jest.config.js file look like?

Answer 2 · 2021-05-26T16:40:12.000Z

Yeah, we have to change the way we are getting the transformer's options. I will try and get this out soon :)

If you're familiar with patch-package, you should be able to patch this module's index.js file.

function createTransformer(src, filename, config) {
  const withFrontMatter = parseFrontMatter(src, config.transformerConfig);
  const jsx = mdx.sync(withFrontMatter);
  const toTransform = `import {mdx} from '@mdx-js/react';${jsx}`;

  return process(toTransform, filename, config).code;
}

Although if you're using babel-jest@27 you might even have to update the babel js import (const { process } = require("babel-jest").default;), just a guess!

Answer 3 · 2021-05-26T16:51:45.000Z

@EvHaus can you try jest-transformer-mdx@3.0.0-beta.0 ? It might work :)

Answer 4 · 2021-05-26T19:27:58.000Z

Nice. jest-transformer-mdx@3.0.0-beta.0 worked for me. Thanks for the super fast turnaround!

Answer 5 · 2021-05-26T19:59:24.000Z

Released in 3.1.0 :)

Answer 6 · 2021-05-26T20:52:27.000Z

I get errors when running the tests on CI :(

So if you hit them, let me know. I'm working on a fix but it's complicated 🙃

Answer 7 · 2021-05-27T15:48:55.000Z

Yeah, I'm getting this on CI with 3.3.0:


Jest: synchronous transformer /myproject/node_modules/jest-transformer-mdx/index.js must export a "process" function.
--
&nbsp; | &nbsp;
&nbsp; | at invariant (node_modules/@jest/transform/build/ScriptTransformer.js:1091:11)
&nbsp; | at assertSyncTransformer (node_modules/@jest/transform/build/ScriptTransformer.js:1097:3)
&nbsp; | at ScriptTransformer.transformSource (node_modules/@jest/transform/build/ScriptTransformer.js:611:7)
&nbsp; | at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:758:40)
&nbsp; | at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:815:19)

But 3.0.0-beta.0 works fine though.

Answer 8 · 2021-05-27T21:57:53.000Z

Nice! If you can stay on the beta that would be great haha. I'll be pushing a new version soon but I need to support configuring the mdx options and that's why you get this error above (noted in #25).