Solution- [eslint] package.json » eslint-config-react-app/jest#overrides[0]: environment key "jest/globals" is unknown

Understanding the Error

This error often arises when ESLint does not recognize the jest/globals environment key in your configuration. Typically, this indicates an issue with your ESLint setup, particularly when integrating Jest testing in your React application.

Common Causes

1. Missing ESLint Plugin: The most common cause is that the required ESLint plugin for Jest is not installed.
2. Configuration Issues: Sometimes, the configuration settings in your package.json or .eslintrc.js file may not be correctly set up.

Solutions

Here are several solutions that have worked for many developers:

1. Install the Required Plugin

Make sure you have the eslint-plugin-jest package installed. You can do this by running:

npm install --save-dev eslint-plugin-jest

This plugin adds Jest-specific linting rules to your ESLint setup.

2. Update Your ESLint Configuration

After installing the plugin, you need to update your ESLint configuration to include Jest environments. If you are using a .eslintrc.js file, it should look like this:

module.exports = {
      env: {
        jest: true,
      },
      plugins: [
        'jest',
      ],
      overrides: [
        {
          files: ['*.test.js', '*.spec.js'],
          env: {
            jest: true,
          },
        },
      ],
    };

If you are configuring ESLint in package.json, ensure it looks like this:

"eslintConfig": {
      "env": {
        "jest": true
      },
      "overrides": [
        {
          "files": ["*.test.js", "*.spec.js"],
          "env": {
            "jest": true
          }
        }
      ],
      "plugins": [
        "jest"
      ]
    }

3. Clear Cache and Restart

Sometimes, changes may not take effect immediately due to caching. Clear your npm cache and restart your development server:

npm cache clean --force
npm start

4. Use eslint-config-react-app

Ensure you are using eslint-config-react-app correctly. If it is missing from your project, add it using:

npm install --save-dev eslint-config-react-app

Make sure to include it in your ESLint configuration if you haven’t done so already.

5. Check Your Node Version

In some cases, the version of Node.js you are using might cause compatibility issues. Ensure you are running a compatible version with your ESLint and Jest configuration. Upgrading Node.js can resolve many underlying issues.

6. Check for Typos

Double-check your ESLint configuration files for any typos or syntax errors that could lead to misconfiguration.

Dealing with ESLint errors can be daunting, but understanding the configuration and ensuring all dependencies are correctly set up can save you a lot of time and frustration. By following the steps outlined in this article, you should be able to resolve the "jest/globals" is unknown error in your React application. Keep experimenting and happy coding!

Resources

• https://stackoverflow.com/questions/58065765/eslint-jest-globals-environment-key-unknown
• https://github.com/facebook/react-native/issues/33955
• https://studygroup.moralis.io/t/development-environment-for-react/19186/45