How to Detect and Remove Unnecessary CSS and JavaScript Code

How to Detect and Clean Unnecessary CSS and JavaScript Code?

In the modern world of web development, the importance of performance and speed-oriented development is increasing. Especially for faster loading of web pages, improving SEO success, and providing a better user experience, cleaning unnecessary CSS and JavaScript code is a critical step. In this article, we will explain in detail and with examples how to identify and clean unnecessary resources in different structures, from PHP-based sites to WordPress-based systems.

1. What is Unnecessary CSS and JS Code?

By "unnecessary" code, we mean resources that are not actively used in the page content but are loaded and rendered by the browser. This code includes:

Style definitions from theme files that have no effect on any element
JS functions that are not linked to any page element
Unused libraries and plugin files that are called but do not work

2. Detection Tools

Important tools you can use to find unnecessary code:

Google Chrome DevTools (Coverage Tab)
UnCSS (CLI or Node based)
PurgeCSS (Very useful for Tailwind projects)
PageSpeed Insights or Lighthouse reports

Example (Coverage with DevTools):

Open your page in Chrome.
Open developer tools with F12.
Command + Shift + P > Type "Coverage" and open the panel.
Click the "Start recording" button and scroll through the page to view the CSS and JS ratios that are not loaded.

3. Cleaning Recommendations for PHP-Based Sites

Especially in custom-written projects, a minimum number of JS and CSS calls should be made before generating the HTML output. Example:

<?php if($sayfa == 'iletisim') { ?>
  <link rel="stylesheet" href="iletisim.css">
  <script src="harita.js"></script>
<?php } ?>

This way, each page only loads the resources it needs.

Also, the following tools can be used for minify and combine operations:

ob_start() + regex cleaning for Minify HTML Output
Automatic build scripts with Gulp or Grunt

4. Removing Unnecessary CSS and JS on WordPress Sites

WordPress themes and plugins generally load too many unnecessary resources. You can use the following methods to remove them:

A) Removing Scripts and Styles with functions.php:

function wp_daha_az_yukleme() {
  if (!is_page('iletisim')) {
    wp_dequeue_style('harita-stili');
    wp_dequeue_script('harita-js');
  }
}
add_action('wp_enqueue_scripts', 'wp_daha_az_yukleme', 100);

B) Plugins like Asset Cleanup or Perfmatters: Allows you to block styles and scripts on a page-by-page basis.

C) CSS/JS Combining and Minify with Autoptimize: You can reduce page sizes by up to 40% with this plugin.

5. Using PurgeCSS in TailwindCSS Projects

In projects developed with Tailwind, all utility classes are compiled by default. However, many of these are not used. To clean this up, the PurgeCSS or Tailwind v3 built-in purge feature is used:

tailwind.config.js
module.exports = {
  content: ['./*.html', './src/**/*.js'],
  theme: { extend: {} },
  plugins: [],
}

With this setting, only the classes used in the page content are included in the build file.

6. Caching and Lazy Load Supports

After completing CSS and JS optimization, page speed should be supported with caching systems:

WP Super Cache / LiteSpeed Cache (WordPress)
Cloudflare CDN and JS Delay (All structures)
Reduce page initial load time with lazy load images

7. Measuring Results with Performance Tests

After the cleaning operations, observe your site with the following tests:

Conclusion

Cleaning unnecessary CSS and JavaScript code in web projects not only speeds up the site but also significantly increases SEO scores. It is possible and beneficial to do this cleaning for all structures, from custom sites developed with PHP to WordPress projects.

If you also want to offer a mobile-friendly site, developed with responsive grid and flex structures, with powerful UI components that enhance user experience, the source codes must be clean, performance-oriented, and optimized.