Setting up Jest with ESM

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 ¹, then add NODE_OPTIONS to the scripts.test in package.json ². See tne Jest documentation for more info (jest.io).

yarn add --dev cross-env

"scripts": {
  "test": "cross-env NODE_OPTIONS=--experimental-vm-modules jest"
}

Add babel-jest (1). Configure Babel (2). We’ll use env.test here so not to interfere with your build process.

yarn add --dev \
  @babel/core \
  @babel/plugin-transform-modules-commonjs \
  babel-jest

module.exports = {
  env: {
    test: {
      plugins: ['@babel/plugin-transform-modules-commonjs'],
    },
  },
}

module.exports = {
  transform: {
    '^.+\\.[t|j]sx?$': 'babel-jest',
  },
}

Add jest-esm-transformer - this is a preset configuration of Babel to support ESM transpilation.

yarn add --dev jest-esm-transformer

module.exports = {
  transform: {
    '\\.m?jsx?$': 'jest-esm-transformer',
  },
}

As of March 2020, using esm is currently not possible. Follow these threads for details.

See buble-jest. Buble is an alternative to Babel. Note that as of 2021, this package hasn’t been updated since 2018.