How to defer parsing of JavaScript in WordPress

JavaScript is integral to the functionality and interactivity of modern websites. However, JavaScript can sometimes slow down your website’s loading time, especially if it’s not optimized properly. When JavaScript is parsed and executed before the critical elements of a webpage are rendered, it can block the page from loading efficiently. This is where deferring the parsing of JavaScript comes into play.

Defer parsing of JavaScript is a technique that allows the browser to delay the execution of JavaScript files until the HTML and CSS are fully loaded. By doing this, users will see content more quickly, improving the overall user experience and enhancing your WordPress site’s performance.

1. Why You Should Defer Parsing of JavaScript

Defer parsing of JavaScript is essential for improving website speed. By deferring the JavaScript execution, you can ensure that the page content loads first, which is crucial for both user satisfaction and SEO. Let’s break down why this is so important.

1.1. Benefits of Deferring JavaScript Parsing

• Improved Page Load Speed: By deferring JavaScript, you let the HTML and CSS load first. This means that your website content appears faster for users, leading to a quicker browsing experience.
• Better SEO: Google uses page speed as a ranking factor. Sites that load faster are more likely to rank higher in search results.
• Enhanced User Experience: Faster loading times result in lower bounce rates, better user engagement, and higher conversions.
• Resource Optimization: Defer parsing reduces resource contention, allowing critical assets to load first, while non-critical scripts are executed later.

2. How to Defer Parsing of JavaScript in WordPress

There are two primary ways to defer parsing of JavaScript in WordPress: using a plugin or modifying the code manually. Both methods are effective, but which one you choose depends on your preferences and comfort with WordPress code.

2.1. Using a Plugin to Defer JavaScript

For most WordPress users, the easiest way to defer JavaScript parsing is by using a plugin. This method does not require any code changes and can be done in just a few clicks.

Install and Activate a Plugin:

• Popular plugins such as WP Rocket and Autoptimize provide the option to defer JavaScript with minimal effort.
• Go to your WordPress dashboard, navigate to Plugins > Add New, and search for the plugin (e.g., “WP Rocket”).
• Install and activate the plugin.

Configure the Plugin Settings:

• In WP Rocket, navigate to Settings > WP Rocket.
• Under the File Optimization tab, you will find an option to Defer JavaScript Loading. Check this option to activate the feature.
• Save the changes.

Clear Cache:

• After configuring the plugin, clear your site’s cache to apply the changes immediately.

Using a plugin is the simplest method, especially if you’re not comfortable working with code. This option also allows you to take advantage of other optimization features available within the plugin.

2.2. Manually Deferring JavaScript in WordPress

If you prefer to handle things manually, you can defer JavaScript parsing by adding a code snippet to your theme’s functions.php file. This requires some technical knowledge but provides more control over which JavaScript files are deferred.

Access the Theme’s functions.php File:

• From the WordPress dashboard, go to Appearance > Theme Editor.
• In the editor, find and open the functions.php file.

Add the Code to Defer JavaScript:

• Add the following code to the functions.php file to defer the JavaScript parsing:

  function defer_parsing_of_js( $url ) {
      if ( is_user_logged_in() ) return $url; // Skip if logged in
      if ( strpos( $url, '.js' ) === false ) return $url;
      if ( strpos( $url, 'jquery.js' ) !== false ) return $url; // Exclude jQuery
      return "$url' defer='defer"; // Add defer attribute
  }
  add_filter( 'script_loader_tag', 'defer_parsing_of_js', 10, 2 );
  

• Save the Changes: After adding the code, click Save to apply the changes to your theme.

This method works well if you need more control over specific scripts and don’t want to rely on third-party plugins. However, always remember to back up your functions.php file before making any changes.

3. Troubleshooting and Common Issues

While deferring JavaScript can boost site speed, it’s important to be aware of potential issues that may arise. Below are some common problems users face and how to resolve them.

• Broken Site Features: Some site elements may rely on JavaScript being loaded immediately. This includes forms, sliders, and other interactive elements.
• Solution: Exclude critical scripts from deferring by adjusting the code in the functions.php file. For instance, jQuery and other essential libraries should not be deferred.

• Layout Issues: Deferring JavaScript could cause some layout problems, particularly if JavaScript is needed for rendering the page correctly.

Solution: Test your site thoroughly on different browsers to ensure that the layout is not affected by the deferring of JavaScript.

• Plugin Compatibility: Certain WordPress plugins that rely heavily on JavaScript might break when their scripts are deferred.

Solution: Identify the problematic plugins and exclude their scripts from being deferred.

To avoid these issues, always test your site thoroughly after making changes to JavaScript parsing. Use tools like Google PageSpeed Insights or GTMetrix to monitor the performance and ensure everything functions smoothly.

Conclusion

Defer parsing of JavaScript is a simple yet powerful optimization technique that can dramatically improve the speed and user experience of your WordPress website. Whether you use a plugin like WP Rocket or Autoptimize or manually adjust your theme’s functions.php file, this strategy helps ensure that your website loads faster, improves SEO, and provides a smoother user experience.

By following the steps outlined in this article, you can optimize the performance of your WordPress site and create a better browsing experience for your visitors. Always test your website after implementing changes to ensure that everything is functioning as expected.