Slaying the Beast: Resolving “Error: ‘console’ is not defined” with ESLint 9 and Jest

Are you tired of staring at the frustrating error message “Error: ‘console’ is not defined” when trying to run your Jest tests with ESLint 9? Well, buck up, buttercup, because today we’re going to tackle this beast and emerge victorious!

What’s behind the error?

Before we dive into the solutions, let’s understand the root cause of this issue. In ESLint 9, the no-undef rule is enabled by default, which means it will throw an error if you try to use an undeclared variable. In this case, the culprit is the console object, which is not explicitly defined in your JavaScript code.

Why is console not defined?

In a browser environment, the console object is globally available and provided by the browser itself. However, in a Node.js environment, where Jest runs your tests, the console object is not automatically defined. This is why ESLint 9 is complaining about it being undefined.

Solution 1: Disabling the no-undef rule for console

The quickest fix is to disable the no-undef rule for the console object specifically. You can do this by adding the following configuration to your .eslintrc file:

{
  "rules": {
    "no-undef": ["error", {
      "typeof": true,
      "global": {
        "console": false
      }
    }]
  }
}

This tells ESLint to ignore the console object when checking for undefined variables. Easy peasy, right?

Solution 2: Defining console globally

If you prefer a more explicit approach, you can define the console object globally in your Jest test environment. Create a new file, e.g., console.js, with the following content:

import console from 'console';

global.console = console;

Then, in your jest.config.js file, add the following setup file:

module.exports = {
  // ... other config options ...
  setupFilesAfterEnv: ['./console.js'],
};

This sets up the console object as a global variable, making it available to your tests and satisfying ESLint’s no-undef rule.

Solution 3: Using the jest/console module

Jest provides a built-in console module that you can use to stub out console methods. In your test files, import the console module like this:

import console from 'jest-mock-extended';

console.log = jest.fn();

This creates a mock console object with a stubbed log method. You can then use this mock console object in your tests, and ESLint will be none the wiser.

Additional Tips and Tricks

Creating a custom console logger

If you want to create a custom console logger for your tests, you can create a new file, e.g., customLogger.js, with the following content:

const customLogger = {
  log: (message) => {
    console.log(`[CUSTOM_LOGGER] ${message}`);
  },
};

global.console = customLogger;

Then, in your jest.config.js file, add the following setup file:

module.exports = {
  // ... other config options ...
  setupFilesAfterEnv: ['./customLogger.js'],
};

This sets up a custom console logger that you can use in your tests, and ESLint will still be happy.

Disabling the no-undef rule for specific files

If you have specific files where you want to disable the no-undef rule, you can add a comment at the top of those files:

/* eslint no-undef: 0 */

This tells ESLint to disable the no-undef rule for that specific file.

Conclusion

There you have it, folks! Three solutions to conquer the “Error: ‘console’ is not defined” issue with ESLint 9 and Jest. Remember, the next time you encounter this error, you can:

• Disable the no-undef rule for console
• Define console globally
• Use the jest/console module

And if you’re feeling extra adventurous, you can create a custom console logger or disable the no-undef rule for specific files.

Now, go forth and slay those errors like a boss!

Solution	Description
Solution 1	Disable the no-undef rule for console
Solution 2	Define console globally
Solution 3	Use the jest/console module

1. ESLint 9 documentation: no-undef rule
2. Jest documentation: configuration options
3. Stack Overflow: related question

Frequently Asked Questions

Error ‘console’ is not defined no-undef with ESLint 9 and Jest? Don’t worry, we’ve got you covered! Here are the top 5 questions and answers to get you out of this sticky situation.