WordPress jQuery not defined and how to fix it

How to fix jQuery is not defined in WordPress

1. Enqueue jQuery properly in functions.php

WordPress comes with jQuery built-in, but you still have to enqueue it properly:

function my_custom_scripts() {
    wp_enqueue_script(‘jquery’);
    wp_enqueue_script(‘my-custom-script’, get_template_directory_uri() . ‘/js/my-script.js’, array(‘jquery’), null, true);
}
add_action(‘wp_enqueue_scripts’, ‘my_custom_scripts’);

Key points:

• Always list ‘jquery’ as a dependency.
• The last argument true ensures the script loads in the footer.

2. Don’t load jQuery from an external source unless necessary

Some themes or developers try to load jQuery from a CDN like Google:

wp_deregister_script(‘jquery’);
wp_register_script(‘jquery’, ‘https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js’);
wp_enqueue_script(‘jquery’);

This can break your site if:

• The CDN is blocked or slow
• It’s loaded after other scripts
• It conflicts with WordPress scripts

Unless you have a good reason, stick with the default WordPress jQuery.

3. Use jQuery instead of $ in your custom scripts

In WordPress, $ is not always available because jQuery is loaded in no-conflict mode.

Instead of this:
$(document).ready(function() {
  // your code
});
Use this:
jQuery(document).ready(function($) {
  // $ now refers to jQuery safely
});

This wrapper makes sure your code works with WordPress without breaking other libraries.

4. Check for plugin or theme conflicts

Sometimes plugins or themes:

• Deregister jQuery by mistake
• Load jQuery in the wrong order
• Override default WordPress behavior

To test this:

• Temporarily switch to a default theme like Twenty Twenty-Four
• Disable all plugins
• Re-enable them one at a time to find the culprit

Once you identify the source, check if there’s an update or contact the developer.

5. Use the right action hook to enqueue scripts

If you enqueue scripts too early (like in init), jQuery might not load in time.

Use the wp_enqueue_scripts action:

add_action(‘wp_enqueue_scripts’, ‘my_custom_scripts’);

This hook ensures scripts are enqueued when WordPress is ready.

6. Defer or async attributes might break jQuery

If you’re using a performance plugin or manually adding async or defer to script tags, it can cause jQuery to load after your scripts that depend on it.

To fix this, exclude jquery.js from deferring or async execution in your performance settings.

7. Check for errors in minified or combined scripts

Minification tools like Autoptimize or LiteSpeed Cache can sometimes break script order.

Try disabling minification temporarily and clear your cache. If the error goes away:

• Adjust the plugin settings to exclude jQuery or control script order
• Clear all cache (site, browser, CDN)