Optimising Page Speed by Reducing Unused JavaScript and CSS

Feb 9, 2025 | Page Speed

At Bold Digital, we believe great marketing starts with a strong foundation – and that foundation is often your website’s performance. As an international marketing agency focused on delivering real results, we blend creative thinking, fresh perspectives, and practical business insight. By breaking down complex technologies, we develop clear messages, eye-catching visuals, and unique brand identities that spark interest in our clients’ products, build brand awareness, and drive enquiries.

One key aspect of delivering exceptional user experiences (and boosting conversions) is optimising your site’s page speed. A common culprit that slows websites down is unused JavaScript and CSS. In this guide, we’ll explore how to identify and reduce these unnecessary elements, keeping your site running at top speed.

1. Why Reducing Unused JavaScript and CSS Matters

Unused JavaScript and CSS can significantly impact your page’s loading times. Every piece of code that must be downloaded, parsed, and executed adds to a visitor’s wait time, increasing the likelihood they’ll bounce away from your site. Slow page speeds can also adversely affect:

  • Search engine rankings: Google and other search engines favour faster websites, meaning poor performance can push your site down the rankings.
  • User experience: Visitors expect pages to load quickly. If your site is slow, user satisfaction plummets, negatively affecting your reputation.
  • Conversion rates: Studies show a direct correlation between page speed and conversions. Faster websites keep potential customers engaged, raising the chances of a sale or enquiry.

2. Identifying Unused JavaScript and CSS

Before trimming the fat, you need to know precisely what’s loading unnecessarily. There are a few tools to help you discover what’s not needed:

  1. Chrome DevTools Coverage
    • Open your website in Google Chrome, then press F12 to open DevTools.
    • Under the ‘Sources’ tab, you’ll find the ‘Coverage’ feature (in some versions, you may need to enable the Coverage panel from the DevTools settings).
    • This will show you how much of each CSS and JS file is actually used when your page loads.
  2. Google Lighthouse (PageSpeed Insights)
    • Run a Lighthouse audit by visiting PageSpeed Insights or using the ‘Lighthouse’ tab in Chrome DevTools.
    • In the report, look for the “Reduce unused JavaScript” and “Reduce unused CSS” opportunities to see which files are flagged.
  3. Third-Party Auditing Tools
    • Tools such as GTmetrix and WebPageTest can also offer insights into file sizes and loading times, helping pinpoint potential areas to clean up.

By gathering data from these sources, you’ll be well-positioned to decide which scripts and styles to keep, remove, or restructure.

3. Effective Strategies to Reduce Unused Code

a) Remove Unnecessary Plugins and Libraries

If you’re using a content management system (CMS) like WordPress, it’s easy to install numerous plugins that load JavaScript and CSS. Regularly audit your site and remove:

  • Inactive or redundant plugins
  • Libraries that aren’t essential (e.g. multiple versions of jQuery, if not strictly needed)

b) Minify and Combine Files

Combining and minifying files is a proven way to reduce page size and improve load times:

  • Minification removes whitespace, comments, and unnecessary characters from code, making files smaller.
  • File combination merges multiple CSS or JavaScript files into one, reducing the number of HTTP requests.

c) Use Conditional Loading

Conditional loading (or lazy loading for scripts and styles) allows you to load resources only when they are needed. For instance:

  • Load scripts conditionally on certain pages instead of site-wide if the functionality isn’t universally required.
  • Defer or async attributes for JavaScript to ensure it doesn’t block initial rendering.

d) Implement Code Splitting and Dynamic Imports

When working with modern frameworks such as React, Vue, or Angular:

  • Code splitting allows you to split bundles into smaller pieces, serving only the parts needed for the current route or page.
  • Dynamic imports let you load modules on demand, ensuring your main bundle remains as light as possible.

e) Inline Critical CSS

Critical CSS refers to the minimum set of CSS required for the first render of your page:

  • Inline these critical styles in the <head> of your HTML document to reduce the initial load time.
  • Defer or lazy-load the rest of your CSS so it doesn’t block the rendering of critical content.

4. Maintaining a Clean Codebase

Optimising your site isn’t a one-off task; it’s an ongoing commitment. Here are some best practices to keep your codebase lean:

  • Regularly audit CSS and JS usage, especially after site changes or updates.
  • Use a style guide or design system to maintain consistency and avoid duplication of styles.
  • Track plugin usage and features to ensure you’re not overloading your site with unnecessary code.

5. The Bold Digital Approach

At Bold Digital, we understand that enhancing technical performance is only one piece of a successful marketing strategy. A fast, efficient website supports the creativity and visual appeal that sets your brand apart. When we break down complex technologies, we develop clear messages and unique brand identities – all while keeping an eye on those ever-important page speeds.

We work closely with clients to:

  • Identify and remove unused or redundant code
  • Implement best practices for conditional loading and code splitting
  • Optimise performance for improved user experience and search engine visibility
  • Craft eye-catching visuals and compelling brand stories to drive enquiries

By combining technical excellence with creative flair, Bold Digital ensures your site not only looks great but also delivers a seamless, fast experience for your audience.

6. Final Thoughts

Reducing unused JavaScript and CSS is a crucial step towards better page speed, enhanced SEO rankings, and a more satisfying user experience. By regularly auditing your site, removing superfluous files, and adopting modern loading techniques, you’ll keep your codebase lean and your load times snappy.

Whether you need guidance on a complete site overhaul or simply want to fine-tune your current setup, Bold Digital is ready to help. By blending creative insight with practical business expertise, we’ll ensure your brand’s online presence is positioned for success – both in performance and in delivering a powerful, memorable message.

Ready to take your site speed to the next level? Contact Bold Digital today and discover how our innovative, results-driven approach can help you achieve a faster, more engaging online experience.