Re-enable ESLint In Lint-staged: A Dev's Guide

Hey everyone, let's dive into a common challenge in modern web development: re-integrating ESLint into our lint-staged configuration after a temporary removal. This is super important for maintaining code quality and catching those pesky errors before they make their way into your codebase. So, let's get started!

The Problem: ESLint and the ESM/CJS Compatibility Tango

As you might know, or if you're new to this, we temporarily sidelined ESLint from our lint-staged setup. This happened during a project's migration using pnpm. The reason? A pesky incompatibility between ESM (ECMAScript Modules) and CJS (CommonJS) during the pnpm migration. This is super crucial; it's all about how JavaScript modules are loaded and used. ESLint was throwing up errors because some of its formatters or plugins were built using ESM, which doesn't always play nice in a CJS context. The specific error that we were getting, as you can see below, highlights the problem:

Error: require() of ES Module ansi-styles/index.js not supported

This means ESLint was trying to load something that was built with modern ESM standards in an older, CJS-based environment, and the two just couldn't talk to each other. Now, for those of you not knee-deep in module formats, just understand that this means our code quality checks weren't running during our pre-commit hooks. Without ESLint, a lot of those helpful checks for code style and potential errors were missing, which made things tricky, to say the least. We needed to get ESLint back up and running, and here's how we plan to do it.

Current State: Prettier Taking the Reins

Right now, our lint-staged configuration is operating solo, with only Prettier handling the formatting. Prettier is a great tool for consistent code formatting, but it doesn't replace ESLint's ability to find actual errors and enforce our code style rules. So, at the moment, our .lintstagedrc.json file looks something like this:

{
  "*.{ts,tsx,js,jsx}": ["prettier --write"],
  "*.{json,md,yml,yaml}": ["prettier --write"],
  "*.{css,scss,less}": ["prettier --write"]
}

As you can see, Prettier is diligently taking care of formatting our code, which is good, but we're missing those all-important linting checks. And that's what we're going to fix!

Proposed Solutions: Picking the Right Path

So, how do we bring ESLint back into the fold? Here are a few potential solutions we can explore:

Option 1: Modernizing with ESLint 9.x

One potential approach involves upgrading to ESLint 9.x and leveraging its flat config system. This can provide native support for ESM, making it possible to sidestep the compatibility issues. It will also involve updating all relevant ESLint plugins to ESM-compatible versions and transitioning from the .eslintrc configuration file to eslint.config.js. It's essentially a modernization play, bringing us up to speed with the latest ESLint features and best practices. This approach is probably the most forward-thinking, but also the most involved, and may require significant changes to the configuration.

Option 2: Dynamic Imports - A Clever Workaround

Another approach is to use dynamic imports in lint-staged. This means changing the configuration to dynamically load ESLint. We could then create a wrapper script to handle bridging the gap between ESM and CJS. This solution offers a more flexible and adaptable approach. While this might mean a bit of extra work, it would allow us to preserve our current ESLint setup while finding a workaround for the compatibility issues.

Option 3: Downgrading Problematic Dependencies

This approach involves carefully identifying the exact dependencies that are causing the ESM issue. The strategy here would be to pin the problematic dependencies to older versions that are CJS-compatible. Although this may introduce a bit of technical debt, it could be the quickest solution, allowing us to restore ESLint functionality without major upgrades or changes.

Implementation Steps: The Road to Re-Integration

Here's how we plan to get ESLint back in action:

1. Identify the Culprit: The first step is to pinpoint the exact package or dependency causing the ESM issue. We'll need to investigate the error messages and the project's dependencies to find the conflicting libraries.
2. Standalone ESLint Check: Next, we'll ensure that ESLint functions correctly outside of lint-staged. This is a crucial step to confirm that the issue is specifically related to the integration and not a general ESLint configuration problem.
3. Update lint-staged: After the standalone test, we'll adjust the lint-staged configuration to use ESLint. This step will involve implementing the chosen solution (e.g., updating ESLint, using dynamic imports, or downgrading dependencies).
4. Thorough Testing: We'll need to thoroughly test our pre-commit hooks to confirm that ESLint runs without errors and that code quality checks are in place.
5. Documentation Update: Lastly, we'll update our project's documentation to reflect any changes to the ESLint and lint-staged setup, making sure that everyone on the team is on the same page.

The Target Configuration: Restoring Code Quality Checks

Once we've successfully re-enabled ESLint, our target configuration will be to restore it to its original state, which should look like this:

{
  "*.{ts,tsx,js,jsx}": [
    "eslint --fix",
    "prettier --write"
  ],
  ...
}

This ensures that both ESLint and Prettier work together seamlessly, providing comprehensive code quality checks and formatting.

Acceptance Criteria: Ensuring Success

To make sure we've successfully re-enabled ESLint, we'll use these acceptance criteria:

• ESLint Runs Successfully: ESLint must run without errors within lint-staged.
• No ESM/CJS Compatibility Errors: We shouldn't see any more of those pesky compatibility issues.
• Pre-Commit Hooks Work: The pre-commit hooks must complete without errors, ensuring a smooth development workflow.
• Enforced ESLint Rules: All our existing ESLint rules must be enforced, maintaining code quality.
• CI/CD Compatibility: The CI/CD pipeline should continue to function without disruptions.

Priority and Related Information

This issue is considered medium priority. While code quality is important, Prettier does offer basic formatting, so the impact is manageable. For more context, check out the following resources:

• PR #82: This is where we first disabled ESLint.
• Issue #77: This highlights the initial testing environment issues.

Wrapping Up

Getting ESLint back in the game is a key step toward maintaining a high-quality codebase. By following the steps above, we can restore those crucial code quality checks and make sure our projects stay top-notch. Let me know what you think and if you have any questions!