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?

Solution 1:

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.

Solution 2:

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)

Solution 3:

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

Solution 4:

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

Should be good!

Solution 5:

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"]
}