Software Engineering in WordPress, PHP, and Backend Development

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How To Identify Anonymous Functions in WordPress

Heads Up! Originally, I wanted to include both how to identify anonymous functions in WordPress and how to unhook them; however, the more I began writing about the topic, the longer the article became.

So I’ve split the content into two articles: This one outlines how to identify anonymous functions registered with hooks. A future article will detail how to de-register said functions.

Previously, I explain how to identify and register anonymous functions in WordPress. As I wrote in the introduction:

As I started writing, it became obvious it’s helpful to understand what PHP does behind-the-scenes when anonymous functions are registered.

So during the first article, I spend time explaining both how anonymous functions are registered – which is clear enough – and how anonymous functions are managed internally by PHP.

If you haven’t read the article, I urge you to do so. But if you’re opting out, the short of it is this:

  1. You register an anonymous function with an associated WordPress hook,
  2. PHP generates an ID via hashing for the anonymous function so that it can be managed internally.

It sound easy enough, but problems arise if you want to programmatically identify those anonymous functions. PHP keeps track of them and the functions fire as they are intended but what happens if you, as a developer, want to access those functions to deregister them?

Identify Anonymous Functions

Before looking how, or if, it’s even possible to deregister anonymous functions, it’s important to know how to identify anonymous functions programmatically. That is, if we know we’re working in an environment where anonymous functions have been registered, how do we actually find them?

This programmer is completely at a loss for where to find an anonymous function.

Again, since these functions are registered with WordPress hooks and since these functions have an ID internally generated by PHP, there’s code we can write to help us understand where these functions are registered.

In the following bit, I’ll show exactly how to do this. This won’t necessarily explain what the code is going nor will it explain who registered the code, but it’ll give us some insight as to what anonymous functions are registered with which hooks.

And that’s a good starting place.

Finding Anonymous Functions

Before using any other specific tools, I’m going to use the following:

It’s not pretty, this isn’t the usual set of tools with which I’d recommend using, but it’s a starting point that’s going to demonstrate the point. In other words, this is a quick and dirty approach to get started.

Further, we’ll be writing anonymous functions in the theme’s functions.php to make it easier to have parity with the content of the article.

With all of that in place, I’ll open functions.php and then add the following code:

add_action('wp_head', 'listRegisteredFunctions', PHP_INT_MAX);
 * Lists all the registered functions.
 * @return void
function listRegisteredFunctions() {
     global $wp_filter;

     echo <<<HTML
     <div style="background:white; font-size:14px;">
    echo <<<HTML

This uses the global $wp_filter object which holds information on all of the referenced actions and filters with WordPress. Note also that I’m setting this up to fire in the wp_head hook and that I’m using PHP_INT_MAX to make sure it has the highest priority (so it fires as late as possible).

Note: I do not recommend nor even suggest using PHP_INT_MAX in a production environment because it makes it incredibly difficult to add anything after that registered hook. This is just for demonstration purposes.

If you run this and then refresh the homepage of your installation, you’re going to see a lot of information. Some of it will make sense, some of it may not. Regardless, it’s going to be a lot of data. And as interesting as it is, there’s not much we can do with it.

If there’s not much to do about it, might as well laugh about it.

To help simplify what it renders, let’s look at something that’s registered with just one of the hooks. Specifically, let’s look and see what’s registered with the wp_enqueue_scripts hook. This hook is one that most anyone who has worked with theme or plugin development has used and something that’s going to have a number of associated callbacks within the context of a theme.

Note, I’m going to use a similar function as used above. I will, however, be changing the actual code in the function. Additionally, note that I have some guard clauses defined for early return so that if nothing is registered with the hook or if there are no callbacks, the function won’t run.

The code looks like this:

add_action('wp_head', 'listRegisteredFunctions', PHP_INT_MAX);
 * Lists all the registered functions.
 * @return void
function listRegisteredFunctions() {
     global $wp_filter;

    if (!isset($wp_filter['wp_enqueue_scripts'])) {

    // Get all functions/callbacks hooked to wp_enqueue_scripts
    $callbacks = $wp_filter['wp_enqueue_scripts']->callbacks;
    if (empty($callbacks)) {

    // ...

It’s not going to render anything yet, though, because I don’t have the code for actually rendering the callbacks and functions associated with the hook. To do that, we can iterate through the callbacks and get each function and its associated priority.

To render that, we need to add:

echo '<pre>';
foreach ($callbacks as $priority => $functions) {
    foreach ($functions as $function) {
        print_r([$function, $function['function']]);
        echo '<br />';
echo '</pre>';

The two important things to take away from the above code are:

  1. I’m adding the function and the $function['function'] to an array that’s dumped by print_r.
  2. $function['function'] contains a reference to the callback function.

In the outer foreach loop, note that $functions is the associative array representing the callbacks hooked to the wp_enqueue_scripts. In the inner loop, $function has information about the callback and $function['function'] is the actual callback itself.

In the environment I’m using to test this code, I’m running the twentytwenty theme and I’ve added the above code to functions.php. If you’re following along with the same – even if it’s a different theme – you’ll likely see something like this written out to the screen:

    [0] => Array
            [function] => twentytwenty_register_scripts
            [accepted_args] => 1

    [1] => twentytwenty_register_scripts

I’ve opted to use this as an example because it’s prefixed with twentytwenty_ meaning it’s likely going to be found within the theme. And when I search for this function in the theme within my IDE, I found the following:

 * Register and Enqueue Scripts.
 * @since Twenty Twenty 1.0
function twentytwenty_register_scripts() {
    // Code remove to keep the code succinct.

add_action( 'wp_enqueue_scripts', 'twentytwenty_register_scripts' );

The important thing to note here is that we see the function twentytwenty_register_scripts is, in fact, registered with the wp_enqueue_scripts hook.

The purpose of looking at this is to see that we’re successfully able to find code that’s registered with our hook of choice. The next challenge, though, is finding anonymous functions that are registered with the same hook.

Sometimes, printing out the code and searching for anonymous functions helps. Supposedly.

You can argue that it’d be more helpful to go ahead and find all anonymous functions registered with this hook but let’s first create out own so we can get an idea as to how this looks.

When doing this, you’ll see how complex, though not impossible, managing anonymous functions can be.

Creating Our Own Anonymous Function

First, comment out the code that’s listing all of the functions registered with the wp_enqueue_scripts hook.

This dude thought registering a function with a hook literally meant he needed a hook.

Next, let’s add our own anonymous functions to functions.php. This will render a message at the top of the page and it will allow us to use previously written code to track track this anonymous function.

add_action('wp_enqueue_scripts', function () {
    echo <<<HTML
        <div style="border:1px outset gray; padding: 1em;background:#ccc;position:fixed;top:0;left:0;z-index:99; width: 100%;">
            This is a a sample anonymous function.
}, 0, 10);

When you refresh the page you’re on, you should see something like this:

The next step will be to run the previously written code and attempt to locate this function.

Now let’s reintroduce the code responsible for printing all of the functions registered with the hook. Assuming you’ve done everything correct, you’ll notice a new piece of data rendered on the page.

Specifically, it’ll read like this:

    [0] => Array
            [function] => Closure Object

            [accepted_args] => 10

    [1] => Closure Object


Assuming there are no other anonymous functions in your code, then this is the function we just wrote and the one we’re looking to manage.

When dressed like this in a place like that, you’re ready to manage all of the code.

So this raises the following two questions:

  1. How can we relate an anonymous function to a specific hook?
  2. How can we de-register this function?

Since we know that PHP generates an internal ID for closures and since we have an anonymous function currently hooked to the wp_enqueue_scripts hook, let’s see what we can do.

Relating Anonymous Functions to Specific Hooks

First, let’s update the code in functions.php so that it dumps all of the information for the closure. I’ll show the code first then explain what it’s doing:

add_action('wp_enqueue_scripts', function () {
    $backtrace = debug_backtrace(DEBUG_BACKTRACE_PROVIDE_OBJECT, 2);
    echo '<pre>';
    echo '</pre>';
    // The original code is here...

Note this part is going to require a bit of functionality offered by PHP. Some of you who have worked with PHP for years may be familiar with this; some of you may not. And if not, that’s okay! I’ll explain it then share a bit more about it.

In the function, I’m grabbing information from one of the built-in PHP functions called debug_backtrace and then I’m using the DEBUG_BACKTRACE_PROVIDE_OBJECT constant to help.

This is a breakdown of each argument and the function to which they are passed:

  • debug_backtrace() is a function in PHP that returns a backtrace, which is an array of associative arrays containing function call information. It provides a snapshot of the call stack at the point where it is called, showing the hierarchy of function calls leading up to that point.
  • DEBUG_BACKTRACE_PROVIDE_OBJECT is a constant flag that can be used as an option when calling debug_backtrace(). When this flag is set, each frame in the backtrace will contain an entry named ‘object’ representing the current object instance.
  • The 2 is an optional parameter specifying the number of stack frames to return in the backtrace. In this case, it limits the backtrace to two frames.
  • And, for what it’s worth, a “frame” refers to a specific level or entry in the call stack (which is, essentially, the order in which functions are called).

This is what a call to this function actually does:

  • The first frame is the frame where debug_backtrace() is called (that is, the anonymous function itself).
  • The second frame is the frame where the function that called debug_backtrace() resides.
  • By limiting the frames to two, you get information about the current function (anonymous function in this case) and its caller.

As I mentioned at the start of this section, using functionality like this is something that comes with having worked with PHP for several years. I don’t remember exactly when I learned it myself. Regardless, that’s an advantage of articles like this, I guess (read: I hope) – it exposes you to new things of which you may not have otherwise been aware.

And yes, de-registering hooks in WordPress is challenging but it’s through these type of facilities that we should be able to do so. When you view this code in your browser, you should see something like the following located in the data you’ve printed to your browser:

array(2) {
  object(Closure)#741 (0) {

Recall from the previous article that PHP does two things when registering callbacks:

  1. Generates an ID for the closure. To generate a unique identifier for this closure, WordPress uses the spl_object_hash() function.
  2. Associates the ID with the callback. The generated closure ID is then associated with the callback function, allowing WordPress to track and manage callbacks even when they are anonymous functions.

And since this is an anonymous function, the ID we see in the print out above is the ID PHP generated when registering the function.

Before We Deregister The Function…

As I stated throughout this article: I wanted to include all of the information in the previous article and this article to explain exactly what PHP is doing, how to locate registered closures, and how to deregister them, but the amount of time it takes to explain how to do all of the above takes longer than I anticipated.

It took so long for this guy to explain the concepts, his audience fell asleep. Maybe his handwriting should be better.

As such, I’m going to pause here. There’s plenty of material to review in terms of the PHP internals as well as work that can be done to inspect your own anonymous functions.

In the next article, I’ll walk through a process – regardless of how manual it is – for how to deregister the functions.

Until then, incorporate some of the code here and also see what other anonymous functions have been registered throughout your codebase.

Identifying and Registering Anonymous Functions in WordPress

Originally, this article started as an explanation for how to remove anonymous functions registered with WordPress. As I started writing, it became obvious it’s helpful to understand what PHP does behind-the-scenes when anonymous functions are registered.

This dude clearly doesn’t understand anonymous functions. The eyes give it away.

Furthermore, this helps give a deeper understanding as to why registered anonymous functions can be problematic and how we can deal with them on a technical level.

Finally, it’s worth noting that I don’t take a hard stance on if anonymous functions should never be used or not. There’s a time and a place where it makes sense, and there’s a time and a place where it doesn’t need to be done. That’s a topic to cover in the future, though.

I’ve mentioned this before, but I’m not in the business of sharing the author of any given tweet [anymore] for the sake of how X/Twitter mobs can behave. Besides, it’s the content of the tweet that warrants a discussion, not the person who said it.

Some time ago, I saw this come across my feed:

I do wish developers would stop using WordPress hooks with (what I think are called) anonymous functions […].

They are very hard if not impossible to unhook.

As mentioned, the how to deregister anonymous functions and the “whether or not this is a good idea” are topics for another post. For now, I want to share what happens whenever an anonymous function is registered with a hook in WordPress.

Named Functions in WordPress and PHP

Brainstorming names for named functions. Naming things is hard.

First, an example:

add_action('admin_init', 'tmAddBackgroundColor');
function tmAddBackgroundColor()
    echo '<style>
            body {
                background-color: #f3f3f3;

In the code above, we’re using a named function – as opposed to an anonymous function – to do the following:

  • add_action('admin_init', 'tmAddBackgroundColor') hooks the tmAddBackgroundColor function to the admin_init action. It tells WordPress to execute the specified function when the admin area is initialized.
  • The actual function adds a custom CSS style to the admin area.

If I was a third-party developer who wanted to remove this functionality, then I’d locate the function and invoke the following call somewhere in my code:

remove_action('admin_init', 'tmAddBackgroundColor');

This is an obvious benefit to named functions. Even if the function is located in a different namespace, it’s possible to remove the action by prefixing the function name with the name of the namespace.

What happens with anonymous functions, though?

Anonymous Functions in WordPress and PHP

You don’t have to name an anonymous function. You might as well just stare at a wall.

If you’re familiar with anonymous functions, then the following code should be clear. If not, though, take a look and I’ll explain what’s happening after the block:

add_action('admin_init', function () {
    echo '<style>
            body {
                background-color: #f3f3f3;

Anonymous functions are generally useful when you have a small, one-time callback that doesn’t need to be referenced elsewhere in your code.

Obviously, the functionality is the same, but it raises the question: How do we call remove_action on this function? That’s something we’re working towards, but first, here’s what happens in PHP whenever you’re working with anonymous functions.

PHP Closures, Closure IDs, and Registration in WordPress

An ID registered for a conference.

Before reading any further, note that a closure in PHP is a way to create an anonymous function.

Just like what’s demonstrated above, it allows us to write a piece of code that can be registered with a hook or, more generally, passed around as a variable. The latter part of this will make sense after we look at what PHP does when an anonymous function is created.

PHP does two things after you register an anonymous function with a WordPress hook:

  1. Generates an ID for the closure. To generate a unique identifier for this closure, WordPress uses the spl_object_hash() function.
  2. Associates the ID with the callback. The generated closure ID is then associated with the callback function, allowing WordPress to track and manage callbacks even when they are anonymous functions.

Given this, another way to write and associate an anonymous function with WordPress would be like this:

$adminInitCallback = function () {
    echo '<style>
            body {
                background-color: #f3f3f3;

add_action('admin_init', $adminInitCallback);

And we can get the ID of the closure as generated by PHP by passing the variable to the spl_object_hash function. For example:

$closureId = spl_object_hash($adminInitCallback);

And that will return the ID that’s generated by PHP and associated with the specific hook in WordPress.

But Still, Deregistering Anonymous Functions?

Though this doesn’t help explain how to deregister anonymous functions, it does help explain how things work within PHP.

This will make it easier to explain ideas around anonymous functions ands hooks in a future post.

Why We Don’t Always Need Do Perform an Early Return

There are a lot of opinions on how return statements should work.

  • Some say that there should be a single point of return in a function,
  • Some day we should return as early as possible,
  • Some day multiple return statements are fine,
  • And some say that, when applicable, return as early as possible.

I’m sure I’m missing some, but all of these are ones I’m sure the majority of you have seen. And though I don’t hold either of these to be law, I think there’s a time and a place for each.

I’m a fan of the early return statement. In my mind, the sooner we can determine we don’t need to do the work of a function, the better we just leave.

For example, say we know if we’re not on a certain page, we can go ahead and leave the function:

In this case, it makes sense because:

  1. You only want to perform work on the plugins.php page,
  2. The amount of work to be done in the function is larger than what should ever fit within a conditional.

But there’s an alternative when the amount of work is less than what’s above.

Continue reading

Use Custom Functions to Determine Which Environment You’re Running Your Code

WordPress provides constants and functions for setting up and checking to see if we’re in development mode.

Specifically, see the following:

But if you’re in a situation in which you’re working on code that’s, say, WordPress-adjacent where it both talks to third-party APIs and services but also sends data to WordPress (or reads data from WordPress), it may be helpful to have another way to determine if your code is running on a local machine.

Use Custom Functions

Case in Point

Perhaps you’re going to be registering a JavaScript file that requires a dependencies that is not available on your local machine. If this is the case, you have a few options:

  1. Find all of the dependencies from the production application and add them to your local machine ignoring whatever side effects may happen,
  2. Remove a call to the dependencies in your code and try to remember to add it back before committing to source code,
  3. Or use a a drop-in function for checking if you’re running the code locally.

Though I know each option has its own tradeoffs, I find myself doing the third option more often than not. All it requires is evaluating the loopback interface and seeing where the script is running.

In the context of PHP, a loopback interface refers to the ability of a script or a server to send requests to itself. So if you check to see if it’s running on, which is an IPv4 variation of localhost or ::1 which is the IPv6 variation of localhost then you can determine how to move foward.

A Simple Example

Here’s my example function:

public function isLocalDevelopmentEnvironment()
    return (
        0 === strcasecmp('::1', $_SERVER['REMOTE_ADDR']) ||
        0 === strcasecmp('', $_SERVER['REMOTE_ADDR'])

Then if you want to use this when, say, enqueuing JavaScript sources in WordPress, you can set up a conditional for dependencies like this:

$dependencies = ['jquery', 'acme-scripts'];
if ($this->isLocalDevelopmentEnvironment()) {
    $dependencies = ['jquery'];

Then you can enqueue the scripts like this:

    $this->jsDir . 'omega.js',

Sure, it’s a simple example but there’s much more that can be done with that single helper function regardless of if you’re working with WordPress, Google Cloud Functions, cloud databases, or more.

There are, of course, much more complicated ways in which custom functions can be written and used. The point isn’t about complexity, though. It’s about thinking through when utility functions like this are helpful and when they should be used.

How You Can Use Ray to Debug Vanilla PHP Utilities

There’s a lot to be said for using a traditional debugger such as Xdebug (and I’m still a fan), but lately, I’ve been writing more generalized PHP utilities that have no front-end and aren’t plugged into any specific application.

That is, I’m using native PHP libraries to run queries against incoming data and help analyze certain aspects of it and output a report.

There’s been a learning curve for a lot of it, but part of the process has included plenty of debugging. And if you’ve read my series on Ray in WordPress, then you know I’m a fan of Ray.

So here’s how you can use Ray to debug vanilla PHP utilities.

In your composer.json file, make sure the following directive is present:

"require-dev": {
	"spatie/ray": "^1.29.0"

Then in the terminal, run the following:

$ composer update

You may need to run $ composer install if you haven’t already, but I’m assuming you’re adding to the file you already have set up.

After that’s done, make sure the following is in your PHP code:


require 'vendor/autoload.php';

// ...

use Spatie/Ray;

At this point, add the following line just to make sure Ray is loading (and make sure the Ray application is actually running). Add the following line:


Then in your terminal run $ php script.php. Assuming all has gone well, you should see the following:

From there, you can use the rest of the tools outlined in the Ray for WordPress series for doing whatever it is you want. Except at this point, you’re just running Ray for debug vanilla PHP utilities.

New context, same functions. Easy enough!

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