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.
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.
I had to add this into my .jestconfig:
"transformIgnorePatterns": [
"<rootDir>/node_modules/(?!lodash-es)"
]
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/"
]
}