Should You Disable jQuery Migrate?

Disabling jQuery Migrate is a common optimisation strategy for WordPress websites, particularly for those focused on performance and modern development practices. To understand why, it's essential to first grasp what jQuery Migrate is and its role in WordPress.

What is jQuery Migrate?

jQuery Migrate is a JavaScript library designed to help websites maintain compatibility when upgrading to newer versions of jQuery. As jQuery evolves, some older features, functions, and behaviours might be deprecated or entirely removed. When a website, theme, or plugin relies on these older functionalities, updating jQuery could break the site.

The jQuery Migrate script acts as a "bridge" or "shim." It restores those deprecated APIs and behaviours, allowing older code to continue functioning on newer jQuery versions. In a development environment, the "development" version of jQuery Migrate can also output warnings to the browser console when deprecated functions are used, helping developers identify and update their code.

WordPress started including jQuery Migrate by default in version 3.6 to ensure backwards compatibility for the vast ecosystem of themes and plugins that might not have kept pace with jQuery updates.

Why Disable jQuery Migrate?

While jQuery Migrate serves a valuable purpose for compatibility, it often becomes unnecessary baggage for modern, well-maintained websites. Here's why disabling it is often recommended:

1. Reduced Page Load Time: jQuery Migrate is an additional JavaScript file that your browser must download, parse, and execute. Even though it's relatively small (typically a few kilobytes), every extra HTTP request and byte of data adds to the overall page load time. Removing it can contribute to a faster loading website.

2. Fewer HTTP Requests: Less overhead means fewer requests to the server, which can be particularly beneficial for users on slower connections or mobile devices.

3. Improved Core Web Vitals: Google's Core Web Vitals metrics (Largest Contentful Paint, First Input Delay, Cumulative Layout Shift) are heavily influenced by page load speed and responsiveness. By reducing the amount of JavaScript that needs to be processed, you can directly improve these scores, which are increasingly important for SEO.

4. Cleaner Code and Fewer Conflicts: If your theme and all your plugins are built with modern jQuery standards, or if they don't rely on jQuery at all, the jQuery Migrate script is essentially dead code. Removing it leads to a cleaner, more streamlined codebase, potentially reducing the chances of JavaScript conflicts.

5. Encourages Modernisation: Forcing your website to run without jQuery Migrate can highlight any outdated code in your themes or plugins. This encourages developers to update their code to modern standards, making your site more robust and less reliant on legacy solutions.

When to Not Disable jQuery Migrate

While there are clear benefits to disabling jQuery Migrate, it's not a universal solution. You should not disable it if:

• You have outdated themes or plugins: If your theme or any active plugins rely on deprecated jQuery functions, disabling jQuery Migrate will likely break their functionality, leading to visual glitches or non-working features on your website. This is particularly true for older or poorly maintained themes and plugins.

• You are using a page builder: Some popular page builders (like Elementor, Divi, WPBakery) might still rely on older jQuery code for their front-end functionalities. Disabling jQuery Migrate could cause issues with your page builder-designed layouts or interactive elements. Always test thoroughly after disabling it.

• You have a custom code that uses deprecated jQuery: If you or a developer has added custom JavaScript code that uses deprecated jQuery features, disabling jQuery Migrate will cause that code to fail.

How to Disable jQuery Migrate

Before attempting to disable jQuery Migrate, it's crucial to back up your website and perform the action on a staging environment first. This allows you to thoroughly test your site for any broken functionalities before making changes to your live site.

Here are the common methods:

1. Using Code in functions.php: This method involves adding a small PHP snippet to your theme's functions.php file (preferably in a child theme or a custom plugin to prevent losing changes on theme updates). This code tells WordPress to remove jquery-migrate from jQuery's dependencies.

    
   PHP

    

   <?php
   /**
    * Dequeue jQuery Migrate script on the frontend.
    */
   function my_dequeue_jquery_migrate( $scripts ) {
       if ( ! is_admin() && isset( $scripts->registered['jquery'] ) ) {
           $script = $scripts->registered['jquery'];
           if ( $script->deps ) { // Check if jQuery has dependencies
               $script->deps = array_diff( $script->deps, array( 'jquery-migrate' ) );
           }
       }
   }
   add_action( 'wp_default_scripts', 'my_dequeue_jquery_migrate' );
   ?>
   

   Explanation:

   • my_dequeue_jquery_migrate(): The custom function.

   • ! is_admin(): Ensures the script is only dequeued on the frontend, not in the WordPress admin area, where it might still be needed for core functionalities.

   • isset( $scripts->registered['jquery'] ): Checks if jQuery itself is registered.

   • $scripts->registered['jquery']->deps = array_diff( $script->deps, array( 'jquery-migrate' ) ): This is the core line. It takes jQuery's dependencies and removes jquery-migrate from that list, effectively preventing it from being enqueued.

   • add_action( 'wp_default_scripts', 'my_dequeue_jquery_migrate' ): Hooks the function into the WordPress script loading process.

2. Using a Code Snippet Plugin: For those less comfortable directly editing theme files, a code snippet plugin (like WPCode or Code Snippets) provides a safe way to add the PHP code from Method 1. Install the plugin, create a new snippet, paste the code, and activate it.

3. Using a Performance Optimisation Plugin: Many popular WordPress performance plugins, such as Perfmatters, WP Rocket, and Asset CleanUp Pro, include a dedicated option to disable jQuery Migrate with a simple toggle. If you are already using one of these plugins, this is often the easiest and safest method. Look for a "Remove jQuery Migrate" or "Disable jQuery Migrate" setting within the plugin's options.

Post-Disabling Testing

After disabling jQuery Migrate, rigorously test your entire website:

• Navigate all pages and posts: Ensure all content displays correctly.

• Test all interactive elements: Check forms, sliders, pop-ups, accordions, tabs, and any other JavaScript-driven features.

• Verify plugin functionalities: Ensure all your active plugins work as expected.

• Check the browser console: Open your browser's developer tools (usually F12 or Cmd+Option+I) and check the "Console" tab for any JavaScript errors. If you see errors related to jQuery, it indicates a dependency on jQuery Migrate.

If you encounter any issues, re-enable jQuery Migrate immediately. The problem is likely due to an outdated theme or plugin that requires the compatibility layer. In such cases, you might need to update the problematic component, find an alternative, or simply keep jQuery Migrate enabled.

SEO Implications

Disabling jQuery Migrate has no direct SEO impact, meaning search engines do not care if the script is loaded or not. However, it provides indirect SEO benefits through performance improvements:

• Faster Page Load Speed: This is a direct factor for Google rankings and significantly enhances user experience, reducing bounce rates.

• Improved Core Web Vitals: As mentioned, better Core Web Vitals scores can lead to improved search visibility.

• Enhanced User Experience: A faster, smoother website experience keeps users engaged, which can signal positive user behaviour to search engines.

In summary, disabling jQuery Migrate is a valuable performance optimisation for many WordPress sites, but it requires careful testing to ensure no existing functionalities are broken. If your site's codebase is modern and well-maintained, you stand to gain from this simple yet effective tweak.