Here are some different ways on how to set up Jest to support ESM. This applies for Jest v25, Node v13, and Babel v7.
Node v14 and Jest v26 support ESM natively with the --experimental-vm-modules
flag.
Install cross-env
:
yarn add --dev cross-env
Add NODE_OPTIONS
to the scripts.test in package.json:
"scripts": {
"test": "cross-env NODE_OPTIONS=--experimental-vm-modules jest"
}
See tne Jest documentation for more info: https://jestjs.io/docs/ecmascript-modules
Add babel-jest
.
yarn add --dev @babel/core @babel/plugin-transform-modules-commonjs babel-jest
Configure Babel. We'll use env.test here so not to interfere with your build process.
// babel.config.js
module.exports = {
env: {
test: {
plugins: ["@babel/plugin-transform-modules-commonjs"]
}
}
};
Configure Jest:
// jest.config.js
module.exports = {
"transform": {
"^.+\\.[t|j]sx?$": "babel-jest"
},
};
You're done.
Add jest-esm-transformer
- this is a preset configuration of Babel to support ESM transpilation.
yarn add --dev jest-esm-transformer
Configure Jest.
// jest.config.js
module.exports = {
"transform": {
"\\.m?jsx?$": "jest-esm-transformer"
},
};
You're done.
As of March 2020, using esm
is currently not possible. Follow these threads for details.
See buble-jest
.
Thanks ! The Method C is not mentioned that much on SO and it was the perfect solution for a node project that doesn't use babel and has mixed esm and commonjs code.