Jest setup "SyntaxError: Unexpected token export"

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.

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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/"
]
}
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最佳答案

I had to add this into my .jestconfig:

"transformIgnorePatterns": [
"<rootDir>/node_modules/(?!lodash-es)"
]
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If none of the other 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.

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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

小开

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"

babel-jest does not transpile import/export in node_modules when Babel 7 is used

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Probably someone finds this useful:

In my case, I have an Angular application that uses lodash-es package. During the testing, I am having the same error as the author.

OPatel's answer worked fine for me with a little tweak (add it to your jest.config.ts):

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

After the changes I also needed to add the "esModuleInterop": true into my tsconfig.spec.json within the compilerOptions property to get rid of the TypeError: cloneDeep_1.default is not a function.

UPDATE:

After the solution above all the lodash methods return LodashWrapper instead of actual values e.g.

const clone = cloneDeep(object); // LodashWrapper

To get rid of this issue I used this solution: https://github.com/nrwl/nx/issues/812#issuecomment-787141835

moduleNameMapper: {
"^lodash-es/(.*)$": "<rootDir>/node_modules/lodash/$1",
}

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