Boosting Performance by Removing Unused Files and Dependencies with Knip and PurgeCSS

As developers, we're constantly striving for better performance. Whether it's faster load times, more responsive UIs, or smaller bundle sizes, performance is a key metric that directly impacts user experience. One overlooked area that can significantly improve performance is cleaning up unused files and dependencies. In this article, I’ll explore how identifying and removing dead code, unused packages, and unnecessary CSS can lead to a leaner, faster project. We'll also take a look at how tools like Knip and PurgeCSS can help automate this process.

Why Cleaning Up Unused Code Matters

Over time, it's easy for projects to accumulate unnecessary files, dependencies, and CSS rules that are no longer in use. These leftovers bloat your project, making it slower to load, harder to maintain, and potentially impacting performance in ways you don’t immediately realize.

By regularly removing unused code, you not only shrink the size of your JavaScript bundles and CSS files but also improve load times, reduce memory usage, and decrease the overall footprint of your application. This practice is especially critical for front-end performance, where every kilobyte counts.

Tools for the Job: Knip and PurgeCSS

Now that we understand the importance of keeping a project tidy, let’s briefly discuss the tools we can use to automate this process. Knip is a tool designed to analyze your JavaScript project and identify unused dependencies and files, while PurgeCSS focuses on cleaning up unused CSS classes from your stylesheets. Together, these tools help ensure that only the code you're actually using makes it to production.

Improving Performance: The Workflow

1. Audit Your Dependencies with Knip The first step to cleaning up your project is auditing your dependencies and modules. Knip scans your project, analyzes the imports, and provides a report of what's in use and what can be safely removed.

Instalation and Setup

npm init @knip/config

Running

npm run knip

Knip generates a report highlighting unused dependencies and files. This allows you to quickly identify which parts of your project are no longer necessary, helping you reduce bundle size and improve performance.

Example output

With this summary, you can safely review your files.

2. Optimize Your CSS with PurgeCSS
CSS, just like JavaScript, can become bloated over time. PurgeCSS is a tool that removes unused CSS selectors from your stylesheets, ensuring that your project only ships the necessary styles.

Instalation

npm i -D @fullhuman/postcss-purgecss postcss

Run PurgeCSS CLI in postbuild

I prefer using it as a post-build script, but you can configure the command for any file you need. Simply specify your build folder and the path to the script.

"scripts": {
      "postbuild": "purgecss --css dist/assets/*.css --content dist/index.html dist/assets/*.js --output dist/assets"
},

With this setup, PurgeCSS will automatically strip away unused CSS classes, leaving you with a much smaller and optimized stylesheet.
Checkout PurgeCSS docs to more details.

3. Regularly Review and Refactor

While tools like Knip and PurgeCSS automate a large part of the cleanup process, regular reviews of your codebase are still essential. Make it a habit to refactor old code, remove unused components, and ensure that your project remains lightweight and easy to maintain. Automating this process with CI/CD pipelines can also help you keep your codebase lean and performant as you continue developing.

Conclusion

Improving the performance of your application isn’t just about writing efficient code; it’s also about keeping your project clean and free of unnecessary files and dependencies. Regularly removing unused code not only reduces the size of your project but also improves load times, simplifies maintenance, and enhances the user experience. Tools like Knip and PurgeCSS make it easier to automate this cleanup process, but the key takeaway is the habit of constantly auditing and optimizing your code.

By adopting this mindset and utilizing these tools, you can ensure your project remains fast, lean, and optimized for the best performance possible.

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