How to use babel-preset-env with Jest

Question

We are in the midst of updating our API, and Henry Zhu from Babel alerted me to this preset called babel-preset-env to replace need for babel-preset-es2015 and babel-preset-es2018.

Now, I am encountering difficulty understanding the simplest way to handle everything.

• Our API uses node v8.x and async/await, native promises
• I want spread operator
• I want pipeline operator
• I want import/export syntax
• I want to support Jest
• I like how babel-node transpiles the API into memory

This will be easier if I just show you the current position of our config:

.babelrc

 {
   "presets": [
     "env",
       {
         "targets": {
           "node": "current"
         }
       },
     "jest"
   ]
 }

package.json

 {
   "scripts": {
     "test": "node --harmony-async-await node_modules/jest/bin/jest.js",
     "start:local": "NODE_ENV=localhost npm run babel-node -- warpcore/server.js",
     "start": "npm run babel-node -- warpcore/server.js",
     "babel-node": "babel-node --presets=es2015,stage-2"
   },
   "dependencies": {
     "babel-polyfill": "^6.23.0"
   },
   "devDependencies": {
     "babel-cli": "^6.24.1",
     "babel-core": "^6.25.0",
     "babel-eslint": "^7.2.3",
     "babel-jest": "^20.0.3",
     "babel-preset-env": "^1.6.0",
     "babel-preset-es2015": "^6.24.1",
     "babel-preset-es2018": "^1.0.0",
     "babel-preset-stage-2": "^6.24.1",
     "jest": "^20.0.4"
   },
   "jest": {
     "testURL": "http://localhost:8080",
     "testEnvironment": "node"
   }
 }

I am uncertain how these things need to be organized to best achieve my bullet list above.

What changes should I make?

• I think the babel-node script needs to change
• I suspect I can remove some of these packages
• I suspect the .babelrc file isn't optimal

Answer 1

If you want to use babel-preset-env as a replacement for babel-preset-es2015 (which is deprecated) with Jest, then you have to make sure that the "modules" property in your "env" configuration is set to "commonjs".

Here is an exemplary configuration:

.babelrc

{     
  "env": {
    "test": {
      "plugins": [
        "transform-class-properties",
        "transform-object-rest-spread"
      ],
      "presets": [
        "jest",
        "react",
        [
          "env",
          {
            "debug": false,
            "modules": "commonjs",
            "targets": {
              "node": "current"
            },
            "useBuiltIns": true
          }
        ]
      ]
    }
  }
}

You can see in env.test, that the preset env (which is the "babel-preset-env" configuration) has "modules" set to "commonjs". That's important, otherwise you will get "SyntaxError: Unexpected token import".

For completeness, here is a simple test:

ExampleButton.test.jsx

import ExampleButton from './ExampleButton';
import React from 'react';
import renderer from 'react-test-renderer';

test('Example Test', () => {
  const component = renderer.create(<ExampleButton />);
  const json = component.toJSON();
  expect(json.type).toBe('button');
});

ExampleButton.jsx

import React from 'react';

class ExampleButton extends React.Component {
  render() {
    return (
      <button onClick={this.props.onClick}>
        {this.props.text}
      </button>
    )
  }
}

export default ExampleButton;

For my Babel setup, I have used the following dependencies:

"babel-core": "6.26.0",
"babel-jest": "21.2.0",
"babel-plugin-transform-class-properties": "6.24.1",
"babel-plugin-transform-object-rest-spread": "6.26.0",
"babel-preset-env": "1.6.1",
"babel-preset-react": "6.24.1",
"jest": "21.2.1",
"react-test-renderer": "16.1.1",

Answer 2

I think I got it working. Here is the solution:

.babelrc

The one posted in the question has a syntax error because the env preset needs to be wrapped in brackets[] (from: http://babeljs.io/docs/plugins/preset-env/)

Correct:

 {
   "presets": [
     ["env",
       {
         "targets": {
           "node": "current"
         }
       }],
     "jest"
   ]
 }

package.json

The one posted in the question has a few things that can be removed:

  {
     "scripts": {
       "test": "jest --verbose",
       "start:local": "cross-env NODE_ENV=localhost babel-node -- app.js",
       "babel-node": "babel-node --presets=env"
    },
    "dependencies": {
      "babel-cli": "^6.24.1",
      "babel-preset-env": "^1.6.0"
    },
    "devDependencies": {
      "babel-eslint": "^7.2.3",
      "babel-jest": "^20.0.3",
      "jest": "^20.0.4"
    },
    "jest": {
      "testURL": "http://localhost:8080",
      "testEnvironment": "node"
    }
  }

Much cleaner in my opinion. You can modulate the presets from the .babelrc file if you want to explicitly include or exclude any, or specify which browsers to support.