Jest setup “SyntaxError: Unexpected token export”

59
votes

I'm implementing tests into an existing project that currently has no tests. My tests are failing to compile node_modules/ imports.

/Users/me/myproject/node_modules/lodash-es/lodash.js:10
export { default as add } from './add.js';
^^^^^^
SyntaxError: Unexpected token export
  
  at transformAndBuildScript (node_modules/jest-runtime/build/transform.js:320:12)
  at Object.<anonymous> (app/reducers/kind_reducer.js:2:43)
  at Object.<anonymous> (app/reducers/index.js:12:47)

The workaround I've found is to 'whitelist' node_modules in package.json jest config like this:

"jest": {
    "transformIgnorePatterns": [
      "!node_modules/"
    ]
  }

This seems like a hack because it takes over 1 minute to run a simple test that imports node_modules/lodash-es/lodash.js.

5
reactjsreduxjestjs
A lot of node modules export ES5 so that jest can run it out of the box without transform. that's why by default jest doesn't transform node_modules. In this case, lodash-es specifically exports es modules, so you HAVE to let jest transform that code. You might be safe if you use "!node_modules/lodash-es" in your transformIgnorePatterns instead so that jest runs babel on lodash-es only. – Lewis Chung

5 Answers

55
votes

I had to add this into my .jestconfig:

"transformIgnorePatterns": [
  "<rootDir>/node_modules/(?!lodash-es)"
]
79
votes

If none of the above solutions worked for you, you can try this in your jest 

"moduleNameMapper": {
    "^lodash-es$": "lodash"
}

It will replace lodash-es with the commonjs version during testing runtime.

23
votes

Posting a more complete answer here:

Jest by default does not transform node_modules because node_modules is huge. Most node modules are packaged to expose ES5 code because this is runnable without any further transformation (and largely backwards compatible).

In your case, lodash-es specifically exposes ES modules, which will need to be built by Jest via babel.

You can try narrowing your whitelist down so Jest doesn't try to pass every JavaScript file within node_modules through babel.

I think the correct configuration in your case is:

"jest": {
  "transformIgnorePatterns": [
    "/!node_modules\\/lodash-es/"
  ]
}
2
votes

For create-react-app users who are looking for a fix, here's what worked for me:

// package.json
...
  "jest": {
    "transformIgnorePatterns": [
      "<rootDir>/node_modules/(?!lodash-es)"
    ]
  },
...

Overriding options in jest.config.js file didn't work for me. Keep in mind that not every option can be overridden, here's a list of supported options: https://create-react-app.dev/docs/running-tests#configuration

0
votes

Renaming .babelrc to babel.config.js and adding transformIgnorePatterns worked for me.

module.exports = {
  "presets": ["@babel/preset-env"]
}

P.S. My jest version is: "jest": "24.9.0"

https://github.com/facebook/jest/issues/6229#issuecomment-419885857