The babel-jest package is a Jest plugin that makes it easy to use Babel to transform your JavaScript tests. It automatically hooks Babel into Jest and compiles files before running them, allowing you to use the latest JavaScript features and syntax in your test files.

What are babel-jest's main functionalities?

Transforming test files with Babel

This configuration in Jest's setup file tells Jest to use babel-jest for transforming any files that match the regex pattern (in this case, any JavaScript files) before running the tests.

module.exports = {
  transform: {
    '^.+\\.js$': 'babel-jest'
  }
};

Using modern JavaScript syntax in tests

With babel-jest, you can write tests using modern JavaScript features like async/await without worrying about compatibility issues.

test('async/await works', async () => {
  const data = await fetchData();
  expect(data).toBe('expected data');
});

Custom Babel configuration

babel-jest allows you to specify a custom Babel configuration to tailor the transformation process to your project's needs.

{
  'presets': [['@babel/preset-env', { 'targets': { 'node': 'current' } }]],
  'plugins': ['@babel/plugin-proposal-class-properties']
}

Other packages similar to babel-jest

Changelog

Source

jest 15.0.1

Updated toThrow and toThrowMatchers and aliased them to the same matcher.
Improvements for watch mode.
Fixed Symbol reassignment in tests would break Jest's matchers.
Fixed --bail option.

Readme

Source

babel-jest

Babel jest plugin

Usage

Make the following changes to package.json:

{
  "devDependencies": {
    "babel-jest": "*",
    "jest-cli": "*"
  },
  "scripts": {
    "test": "jest"
  },
  "jest": {
    "scriptPreprocessor": "<rootDir>/node_modules/babel-jest",
    "testFileExtensions": ["es6", "js"],
    "moduleFileExtensions": ["js", "json", "es6"]
  }
}

And run:

$ npm install

And you're good to go!

Using experimental stages

By default, babel-jest will use Babel's default stage (stage 2). If you'd like to use one of the other stages, set the environment variable:

BABEL_JEST_STAGE

And then you can modify the test command in package.json like so:

{

  // Normal pakcage.json stuff,

  "scripts": {
    "test": "BABEL_JEST_STAGE=0 jest"
  },

  // Normal pakcage.json stuff
}

FAQs

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Package last updated on 03 Apr 2015

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