To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config

Question

I running jest test file and getting the following error:

 ● Test suite failed to run

    Jest encountered an unexpected token

    Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.

    Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.

    By default "node_modules" folder is ignored by transformers.

    Here's what you can do:
     • If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to enable it.
     • If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.

    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/configuration
    For information about custom transformations, see:
    https://jestjs.io/docs/code-transformation

    Details:

    /Users/test/dev/pm/client/node_modules/spacetime/src/index.js:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){import Spacetime from './spacetime.js'
                                                                                      ^^^^^^

    SyntaxError: Cannot use import statement outside a module

       6 | import search from '../../assets/images/search.svg';
       7 | import Dropdown from 'react-bootstrap/Dropdown';
    >  8 | import spacetime from "spacetime";
         | ^
       9 | import languages from "../../libraries/languages/language-list";
      10 | import { Rating } from 'react-simple-star-rating';
      11 |

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1728:14)
      at Object.<anonymous> (src/components/Mentor/MentorList.js:8:1)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        2.097 s

I tried to fix it by adding the following to package.json, but that didn't work:

  "jest": {
    "transformIgnorePatterns": [
      "node_modules/(?!spacetime)"
    ]
  },

Can someone please help?

Younglove

See related question – Elva

Answer 1

spacetime package main file is ES6 module. See node_modules/spacetime/src/index.js, this is the main file the package exports.The package.json of spacetime include "main": "src/index.js".

By default "node_modules" folder is ignored by transformers.

You don't need to add transformIgnorePatterns configuration for jest config, the node_modules folder is ignored by transformers.

But this is not the issue.

The issue is jest does not parse es6 import/export statement by default, even though it uses babel.

Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.

We need to transform the es6 import and export syntax.

option 1. Add babel config

option 2. Use ts-jest preset for jest.

jest.config.js:

module.exports = {
  preset: 'ts-jest/presets/js-with-ts',
  testEnvironment: 'jsdom'
};

option 3. Use esbuild-jest

jest.config.js:

module.exports = {
  testEnvironment: 'jsdom',
  transform: {
    '\\.[jt]sx?$': 'esbuild-jest',
  },
};

Miltie

hi Thanks for the amazing answer. Can you please look at this question? #71065498 – Younglove

I added the configurations that you specified but my jest.config.js file is being ignore. Please help! Thanks. – Younglove

So this didn't work for me. Is there another solution? @slideshowp2 – Younglove

@slideshowp2 You misunderstood the issue completely. Because node_modules are ignored, any package being imported in a test does not have its syntax transformed (even if the parent file is transformed with babel as you suggested). Therefore if there is an import statement in a package in node_modules and it's not transformed it will of course throw Cannot use import statement outside a module. As OP said, transformIgnorePatterns is supposed to provide a way to specify which directories are ignored, but it doesn't work. – Mitre

@BennySchmidt, do you know if it's worth trying a regex excluding the packages to still transpile in the transformIgnorePatterns ? This is suggested by the jest doc: jestjs.io/docs/… I did not succeed to have it working on my side so far... – Clichy

Answer 2

I am not sure is this question still relevant. What I see there's a slight error on your transformIgnorePattern entry.

  "jest": {
    "transformIgnorePatterns": [
      "node_modules/(?!(spacetime)/)"
    ]
  }

Please mind the parentheses around the spacetime. I was reading the part transformIgnorePattern part from Jest docs, So with having a fresh eye, just spot the missing parentheses.

This is the quote from Jest Docs

In the example below, the exclusion (also known as a negative lookahead assertion) for foo and bar cancel each other out:

{
 "transformIgnorePatterns": ["node_modules/(?!foo/)", >"node_modules/(?!bar/)"] // not what you want
}``` 

Chemarin

Answer 3

I found a few things that can cause this issue, and cause transformIgnorePatterns to seem not to work:

• Getting the syntax of the transformIgnorePatterns regex wrong. You’re trying to tell jest to ignore (ie not transform) almost everything in node_modules, except for the problem dependency, and maybe also its transitive dependencies. So it’s a complicated regex. I used an online regex checker to get mine right.
• Specifying transform in the jest config and forgetting to include the default babel-jest
• Specifying a --config= on the jest command line, so I was changing the wrong file. This is a silly mistake, but I made it - so others might too!
• Not having a babel.config.js. It has to be a babel.config.js, and .babelrc won’t do, even though it should be equivalent.

Once I’d fixed all of those issues, I found that the error moved around, and I had to add a few extra modules into my regex, since they were imported by the original dependency.

Agama