How to override parent theme functions in a child theme

Three different methods to override parent theme functions

The best practice to customize your WordPress (parent) theme and override template files or functions is by using a child theme. We’ve already pulished a basic tutorial on how to create and use child themes. However, while overriding template files in a child theme is easy, overriding parent theme functions in a child theme takes some additional efforts if you want to do it the right way.

Child Theme Tutorial
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When it comes to overriding parent theme functions in your child theme, you have to keep track of a couple of things. Beforehand, it is important to know that all functions in your parent theme are running as well when using a child theme. However, functions in your child theme will be loaded first. With this in mind, there basically are three common ways to override parent theme functions in WordPress while using a child theme based on the given scenario:

  • Taking advantage of pluggable functions – an easy way for overriding parent theme functions but only possible if your parent theme is making use of pluggable functions.
  • Specify priority for function execution – you can determine in which order functions are running in WordPress – but sometimes setting the priority isn’t enough to override functions.
  • Making use of hooks, actions and filters – applies when you want to prevent the outcome of a parent theme function taking effect on your website. After you’ve unhooked the parent theme function, you can add new functionality with your new custom function in your child theme.

1. Taking advantage of pluggable functions

Let’s start with pluggable functions. What does the word pluggable actually mean? Pluggable means that the parent theme function is wrapped in a function_exists() if-condition to check whether the function already exists – if so, the function will not be executed, otherwise WordPress will run the function. Here is an example of a pluggable function with conditional tag:

Example of a pluggable function

if (!function_exists('my_parent_theme_function')) {
    function my_parent_theme_function() {
        // Code of your pluggable function
    }
}

Now remember what was mentioned earlier – child theme functions are being executed first in WordPress. That means you can simply take the function from the parent theme, without the conditional tag, put it in file functions.php of your child theme and let it run whatever you like. That way the function in your child theme will be executed instead of the function in your parent theme. And this is what the function without the if-statement would look like in your child theme:

Example of overriding pluggable function

function my_parent_theme_function() {
    // Code of your new function in the child theme
}

Please note, taking advantage of pluggable functions is not always advisable. Let’s say you want to override certain functionality within a pluggable function. Overriding the entire parent function within your child theme could lead to problems in the future. If the parent function is updated one day, your child theme will load the old version of the function and override the new one, which may lead to compatibility issues or even security vulnerabilities on your WordPress website. For alternatives please have a look at: Making use of hooks and filters.

2. Specify priority for function execution

In case the WordPress theme you are using does not provide pluggable functions or those functions you are aiming to override are not pluggable, you need to help yourself with other methods. Functions in WordPress are being executed in a certain order and you can specify the priority for your custom function to determine the order of execution. By default, when nothing else is defined, this priority is 10. Here is an example of a function with default priority 10:

Example of function with default priority

function my_parent_theme_function() {
    // Code of your parent theme function
}
add_action('after_setup_theme', 'my_parent_theme_function');

In the following example you can define a higher priority of 20 for your function in a child theme, so the function with higher priority will run later and override the function in the parent theme:

Example of function with defined priority

function my_child_theme_function() {
    // Code of your child theme function
}
add_action('after_setup_theme', 'my_child_theme_function', 20);

3. Making use of hooks, actions and filters

If for some reason you want to remove the outcome of a certain function for good, then using priorities is not sufficient and not necessarily the correct approach. Furthermore, if there are no pluggable functions available or if you do not want to override an entire pluggable function, you might want to take a close look at actions and filters.

With this approach you will remove the outcome of the parent theme function from the action hook it is attached to and thus prevent it from affecting your website. After that you can code custom functionality in your child theme and hook it accordingly for use on your website. Here is an example of a function attached to the after_setup_theme action hook:

Example of function attached to hook

function my_parent_theme_function() {
    // Code of your parent theme function
}
add_action('after_setup_theme', 'my_parent_theme_function');

To override this function in your custom child theme, you first would need to use remove_action() or remove_filter(), depending on what is given to unhook the function in your child theme. In this case the function has been added with add_action(), so you need to use remove_action():

Example of removing function from hook

remove_action('after_setup_theme', 'my_parent_theme_function');

With this in mind, you can now code a custom function in your child theme to unhook the function from your parent theme. It’s important to know that in order to unhook the parent theme function, you would either need to use an action hook that is called after the hook which is being used in the parent theme or you would need to work with priorities instead to ensure that your child theme function is executed after the parent theme function in order to unhook the function accordingly.

Example of unhooking the parent theme function

function remove_my_parent_theme_function() {
    remove_action('after_setup_theme', 'my_parent_theme_function');
}
add_action('wp_loaded', 'remove_my_parent_theme_function');

After you’ve successfully removed the parent theme function, you can know code a new custom function in your child theme based on your personal requirements.

Conclusion: Overriding parent theme functions in a child theme

To give a résumé, all these three methods can be used, but it always depends on the given scenario. Removing functions from hooks takes a little more effort, but is perfect for selectively overriding parent theme functions in child themes without the need to override entire pluggable functions. While keeping future theme compatibility and security in mind, using pluggable functions to override parent theme functions is advisable if the function runs a simple process only.

Have you ever tried to override parent theme functionality in a child theme? Which approach have you used and what were the issues you were facing while overriding the parent theme? We’re excited to learn more about your experiences while coding child themes in the comments.

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10 Comments

  1. I had doubts about default priority and attached to hook function. Now, I’m clear. Thank you ALINE for your great help.

  2. Hi, I’m going to use the third method for overriding a function in my parent theme. But I can not find something like this line of code in parent theme:

    add_action('init', 'parent_function');

    Would you please tell me what is wrong with my theme? How can I use the third way? Thanks.

    • Hi Jack, you would need to check how the WordPress theme you’re using has been coded. If the theme doesn’t make use of hooks to implement functionality, then you usually can’t unhook and you would need to use a different approach of overriding parent theme functionality.

  3. I have used the priority for function execution, because the function I wanted to override is not pluggable. It was in the inc/custom-header.php file. I had to put my replacement function in the functions.php file in my child theme to make it work.

  4. Hello Aline, thanks for this very clear explanation! In my child theme, I would like to override a certain pluggable function in /wp-includes/pluggable.php. So far, I haven’t succeeded: the site just goes blank. Is it even possible and if so, could you please give me some pointers?

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