Jest not parsing es6: SyntaxError: Unexpected token import

Question

I am trying to setup Jest with my webpack project. When I run my tests, Jest complains it cannot read es6 code. Babel seems to not transform my test files.

I have tried

Answer 1

I have some useful information that can be used as a reference for those who see this problem later.

By default, transformIgnorePatterns in jest config was ["/node_modules/", "\.pnp\.[^\/]+$"]

If some guys issue was caused by some code in node_modules and do not overwrite this value, babel-jest still not working.

Maybe the correct value like this "/node_modules/(?!(your-third-part-es-module-code|others-es-lib))"

Answer 2

You need to do two things:

1. Create a Babel config file (babel.config.js):

   This is necessary because babel-jest relies on a traditional Babel config file, not webpack. Since version 7 Babel has supported JS configs as babel.config.js.

   When using a JS Babel config (as opposed to a .babelrc, for example) Jest also compiles modules in node_modules. AFAIK by convention this must be in the root of your project, alongside the jest configuration file.

   Here is a config based on the Babel options in your webpack.config.js file:

   // babel.config.js
   module.exports = {
     presets: [
       '@babel/preset-env',
       '@babel/preset-react',
       '@babel/preset-flow',
     ],
     plugins: [
       'babel-plugin-styled-components',
       '@babel/plugin-proposal-class-properties',
     ]
   }
   

2. Install the babel-core bridge version:

   npm install babel-core@7.0.0-bridge.0 --save-dev
   

   From github.com/babel/babel-bridge:

   This repo holds what we're calling a "bridge" package that is meant to ease the transition for libraries that use "babel-core" as a peer dependency for Babel 6.

   The issue with Babel 7's transition to scopes is that if a package depends on Babel 6, they may want to add support for Babel 7 alongside. Because Babel 7 will be released as @babel/core instead of babel-core, maintainers have no way to do that transition without making a breaking change. e.g.

Answer 3

I ran into a similar situation where I wanted to test a React component .js file with jest, but it was failing because the component imported a .css stylesheet. I was using Babel with Webpack.

As per the accepted answer @sdgluck, I had to add a babel.config.js:

1.

module.exports = {
    presets: ['@babel/preset-env', '@babel/preset-react']
};

2. I also installed babel-jest as a dev-dependency

3. Then I read through the jest webpack guide

4. Which led me to adding a "jest" property to my package.json which mocks files and stylesheets:

"jest": {
    "moduleNameMapper": {
      "\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/__mocks__/fileMock.js",
      "\\.(css|less)$": "<rootDir>/__mocks__/styleMock.js"
    }
  }

5. Then I had to create the mocked files at the specified paths (you can use any path you want, those are just from their docs):

// __mocks__/styleMock.js

module.exports = {};

// __mocks__/fileMock.js

module.exports = 'test-file-stub';

Then it worked :)