Does Jest support ES6 import/export?

If I use import/export from ES6 then all my Jest tests fail with error:

> Unexpected reserved word

I convert my object under test to use old school IIFE syntax and suddenly my tests pass. Or, take an even simpler test case:

   var Validation = require('../src/components/validation/validation'); // PASS
   //import * as Validation from '../src/components/validation/validation' // FAIL

Same error. Obviously there's a problem with import/export here. It's not practical for me to rewrite my code using ES5 syntax just to make my test framework happy.

I have babel-jest. I tried various suggestions from GitHub issues. It is no go so far.

File package.json

 "scripts": {
    "start": "webpack-dev-server",
    "test": "jest"
  },
      "jest": {
        "testPathDirs": [
          "__tests__"
        ],
        "testPathIgnorePatterns": [
          "/node_modules/"
        ],
        "testFileExtensions": ["es6", "js"],
        "moduleFileExtensions": ["js", "json", "es6"]
      },

File babelrc

{
  "presets": ["es2015", "react"],
  "plugins": ["transform-decorators-legacy"]
}

Is there a fix for this?

From my answer to another question, this can be simpler:

---

The only requirement is to configure your test environment to Babel, and add the ECMAScript 6 transform plugin:

---

Step 1:

Add your test environment to .babelrc in the root of your project:

{
  "env": {
    "test": {
      "plugins": ["@babel/plugin-transform-modules-commonjs"]
    }
  }
}

Step 2:

Install the ECMAScript 6 transform plugin:

npm install --save-dev @babel/plugin-transform-modules-commonjs

---

And that's it. Jest will enable compilation from ECMAScript modules to CommonJS automatically, without having to inform additional options to your jest property inside package.json.

UPDATE 2020 - native support of ECMAScript modules (ESM)

---

According to this issue, there is native support of ESM from [email protected]. So you won't have to use babel anymore. At the time of writing this answer (05/2020), to activate that you need to do three simple things:

• Make sure you don't transform away import statements by setting transform: {} in config file
• Run node@^12.16.0 || >=13.2.0 with --experimental-vm-modules flag
• Run your test with jest-environment-node or jest-environment-jsdom-sixteen.

So your Jest configuration file should contain at least this:

export default {
    testEnvironment: 'jest-environment-node',
    transform: {}
    ...
};

And to set --experimental-vm-modules flag, you will have to run Jest as follows:

node --experimental-vm-modules node_modules/jest/bin/jest.js

Also note in the Github issue that this approach does not yet support the jest object. So you may need to import it manually:

import {jest} from '@jest/globals'

(I hope this will change in the future)

For an updated configuration, I'm using https://babeljs.io/setup#installation

Select JEST and be happy:

As a reference, the current configuration:

npm install --save-dev babel-jest

In your package.json file, make the following changes:

{
  "scripts": {
    "test": "jest"
  },
  "jest": {
    "transform": {
      "^.+\\.jsx?$": "babel-jest"
    }
  }
}

Install babel preset:

npm install @babel/preset-env --save-dev

Create a .babelrc file:

{
  "presets": ["@babel/preset-env"]
}

Run your tests:

npm run test

In package.json, kindly set like this one: "test": "node --experimental-vm-modules node_modules/.bin/jest"

Should be good!

It's a matter of adding stage-0 to your .babelrc file. Here is an example:

{
  "presets": ["es2015", "react", "stage-0"],
  "plugins": ["transform-decorators-legacy"]
}

I encountered the same issue.

These are what I did:

yarn add --dev babel-jest @babel/core @babel/preset-env

Make file jest.config.js in rootDir.

module.exports = {
    moduleFileExtensions: ["js", "json", "jsx", "ts", "tsx", "json"],
    transform: {
        '^.+\\.(js|jsx)?$': 'babel-jest'
    },
    testEnvironment: 'node',
    moduleNameMapper: {
        '^@/(.*)$': '<rootDir>/$1'
    },
    testMatch: [
        '<rootDir>/**/*.test.(js|jsx|ts|tsx)', '<rootDir>/(tests/unit/**/*.spec.(js|jsx|ts|tsx)|**/__tests__/*.(js|jsx|ts|tsx))'
    ],
    transformIgnorePatterns: ['<rootDir>/node_modules/']
};

Then make file babal.config.js in rootDir.

Go like this:

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

In addition to installing babel-jest (which comes with Jest by default now) be sure to install regenerator-runtime.

To add support for React and react-testing-library it may be useful to eject CreateReactApp and take all needed Jest configuration from the package.json. It is ready to use with another bundler, Rollup in my case.

Below is how I setup jest, typescript and ES Modules for my project.

jest.config.js

/**
 * @type {import('ts-jest/dist/types').InitialOptionsTsJest} 
 * To configure ESM support, see: https://kulshekhar.github.io/ts-jest/docs/guides/esm-support
 * 
 **/
export default {
    preset: 'ts-jest/presets/default-esm',
    testEnvironment: 'node',
    extensionsToTreatAsEsm: ['.ts'],
    globals: {
        'ts-jest': {
            useESM: true
        }
    },
    setupFiles: ['<rootDir>/__tests__/setup.ts'],
};

tsconfig.json

{
    "compilerOptions": {
        "target": "ESNext",
        "module": "ESNext",
        "outDir": "./dist",
        "moduleResolution": "node",
       // "strict": true,
        "esModuleInterop": true,
        "inlineSourceMap": true,
    }
}

package.json scripts and devDependencies

"scripts": {
    "start": "node ./dist/server.js",
    "dev": "tsc-watch --onSuccess \"node ./dist/server.js\"",
    "test": "cross-env NODE_OPTIONS=--experimental-vm-modules jest"
  },
"devDependencies": {
    "@jest/globals": "^27.4.4",
    "@types/express": "^4.17.13",
    "@types/jest": "^27.4.0",
    "@types/supertest": "^2.0.11",
    "cross-env": "^7.0.3",
    "supertest": "^6.2.1",
    "ts-jest": "^27.1.3"
  }

__tests__/setup.ts

import dotenv from 'dotenv';


dotenv.config({
    path: './.env.test'
});