Four Ways to Extend WordPress Functionality: A Guide to Adding Custom Functions

Discover How to Add Customization to WordPress: A Practical Guide

As a WordPress back-end developer with many years of experience, I've tried a variety of ways to customize WordPress to meet my own and others' specific needs. One of the most common ways is to create your own WordPress Custom Features plugin. But as you'll see in this article, this is not the only option, nor is it always the best option.

While this guide is primarily geared toward developers, project managers can also learn how these strategies meet the needs of their teams, and when and how to utilize them effectively.

Here are a few ways I personalize WordPress:

1. Add the code to your theme's functions.php file.
2. Create a WordPress plugin dedicated to customization.
3. Use plugins to manage and apply custom snippets.
4. Personalize it with essential plug-ins.

Now, let's explore each method in detail

Add the code to Functions.php

In the "early" days of WordPress, when most sites were written in PHP, the fastest way to change the functionality of a site was to add code to the theme's functions.php file.

You can still do this now, and if you're willing to take the risk, you can edit it directly in the theme file editor in your WordPress dashboard.

Over time, I've gone from being most comfortable using the WordPress functions.php file to customize the site to being least inclined to use it.

The main problem is that the functions.php file is attached to the theme. This means that if you're not using a theme that was customized specifically for you and the theme undergoes an update, all the personalization you've done will be lost.

One solution is to create a child theme so that you can keep changes related to the parent theme without affecting the theme itself.

Now, I try to avoid adding too much custom code to the functions.php file, mainly because a lot of that code is better suited to plugins, which are often used to add new functionality to a site rather than just change the style of the theme.

There are two other cases where I would consider writing custom code into the functions.php file:

1. This code is specifically for my own custom themes or child themes.
2. I need to test some changes quickly, as access to the functions.php file is usually easy.

Keep in mind, however, that you shouldn't pile too many changes into the functions.php file or the file will become very complicated. Especially if there are multiple PHP files and other types of files that need to be used, I would choose to create a specialized WordPress Custom Functions plugin to manage these changes.
Writing custom function plug-ins

As I mentioned before, most of the code I add to the site is used to build or enhance features that are not related to the theme.

Whenever I decide to add more custom content to a website, I start creating a custom features plugin. I usually name the plugin after the site, for example, for WP Mayor I would create a plugin called "WP Mayor Custom Features".

Naming is really important! First of all, it lets other administrators of the site know at a glance that the plugin was designed specifically for this site and is primarily used to place changes specific to that site.

Second, keeping the naming of plugin folders and files unique will prevent your plugin from being accidentally replaced by other plugins with the same name in the WordPress.org plugin repository.

Creating a WordPress Custom Features plugin is actually quite simple. You just need to start in the wp-content/plugins directory. However, you should create a new folder first, usually you will need more than one file to organize your code and you may need to add JavaScript and CSS files as well.

Taking our example, we now have a new plugin folder wp-content/plugins/wp-mayor-custom-functions and a main plugin file wp-mayor-custom-functions.php.

Now we need to add a header to the file so that WordPress recognizes it as a plugin. While just filling in the "Plugin Name" will get it basically working, let's look at a more detailed example:

/**

* Plugin Name: WP Mayor Custom Function

* Plugin URI: https://wpmayor.com

* Description: All the cool features we custom-built for us.

* Version: 1.0.0

* Requires at least: 6.2

* Requires PHP: 8.1

* Author: Thomas Maier

*/

After doing this, our plugin should appear on the "Plugins" page of the WordPress dashboard.

Now we can start adding real PHP code to the file.

Tip: If I can't access the site via FTP, or I just want to save myself the trouble, I'll use a plugin called Pluginception to get started quickly. I can then add more code in the plugin editor in the WordPress dashboard.

You're probably wondering if all site-specific code should be in a custom feature plugin?

It really depends on the situation. If I know that certain custom codes will be used in multiple projects, I put them in different plugins. However, code that is specifically designed for a particular site, I put in the same plugin. This way, I can reduce the number of plugins I need to maintain.

Sounds fairly simple, right? Well, having managed one of the larger plugin companies and made hundreds of tweaks to multiple sites over the past few years, I've found that these custom plugins are still usually better suited for developers. So, let's explore another approach in the next section.

Use the code snippet plugin to manage

I'm in the habit of consolidating all common code into a single custom feature plugin. That way, any changes to the plugin, such as redirecting a blank cart page to a price page, adding promotional information or Black Friday specials, are clearly documented and stored in their own easily-understood files with their own names.

This approach is "well documented" and "easy to read" for those who have direct access to the code.

But I've found that while I'm always making changes or answering questions about it, it's not the most efficient or sustainable way to manage a lot of customization.

As more and more people start managing stores and websites, I want them to be able to easily understand these changes, rather than relying on a knowledge base page dedicated to updates.

The solution is to use a custom feature plugin to manage code snippets in the WordPress dashboard.

My personal preference is to use the free Code Snippets plugin, but of course there are other options.

After installing this plugin, there will be an additional menu item in the dashboard dedicated to listing all code snippets.

The changes are now visible to anyone with administrative privileges. I gave each code snippet a descriptive name, detailed it with a comment area, and labeled the different changes.

I usually use the name of the plugin or theme in question, as well as the part of the site it relates to as tags, such as "WooCommerce" and "checkout page".

If you pick names that are easy to understand and a well-organized structure, then anyone should be able to find and understand the tweaks, myself. I even use this method on my personal website because it makes everything so much easier.

Using the Custom Functions plugin is especially handy for code snippets that you only need on a temporary basis, such as some cleanup scripts that are executed occasionally or some actions that affect the front-end (such as launching a promotional campaign).

Is this safe?

Normally, WordPress allows any user with "admin" privileges to edit plugin and theme files on the backend. The same is true for plugins with custom code. So, the old security measure of granting only the necessary permissions to each user is still important.

For developers, using plugins to manage code means that some early hooks may not be available when the page loads because the plugin needs to be loaded first. If you need to load your custom code before all other plugins, you may want to look at the so-called MU Plugins option.
Customize WordPress Features with Essential Plugins

The so-called "must-have" plugins are a special type of plugins.

They run before all the other normal plugins, so I often use them to control whether certain plugins are turned on or off on a particular page, such as to speed up certain features or improve the efficiency of calls to admin-ajax.php.

An important feature of "must-have" plugins is that they are automatically enabled and cannot be disabled or modified via the WordPress dashboard. This makes them an ideal option for storing core code that even administrators can't change.
Creating the necessary plug-ins

The "Required" plugin is placed in the wp-content/mu-plugins folder. New installations of WordPress don't have this folder by default, but sometimes some plugins or hosted services automatically add content here.

go mu-plugins To add a new plugin to your folder, you need to create a PHP file on your computer with the custom plugin's header information as I showed before. This time, you don't need to worry about naming uniqueness, because "must-have" plugins are not automatically updated.

Once you are happy with your new custom feature plugin, you can manually upload it via FTP to the wp-content/mu-plugins Folder. If this folder does not already exist, create a new one.

Although you can't change the "required" plugins through the WordPress admin panel, you can see them in the "Plugins > Required Plugins" section.

I used to like to customize my WordPress site in a special way, but now I don't like it so much. The problem is that all the changes are in a file called functions.php and this file belongs to the theme of the site. If the theme is not made by me and is updated, then all the tweaks I made disappear.

The solution was to make a 'child theme' so I could keep all the changes associated with the original theme.

I don't add a lot of custom code to the functions.php file anymore, as I find that most of the time these changes should be done through plugins, which add new functionality to the site rather than just changing the look and feel.

There are two cases where I also write custom code in the functions.php file:

1. When the code is specifically for my custom theme or child theme.
2. When I wanted to quickly test some changes because it was easy to access and modify the functions.php file.

But remember, you shouldn't pile a lot of changes into this file. If the file is too complex, it will be hard to manage. Especially if there are a lot of PHP files and other types of files that need to be used, I would choose to create a specialized WordPress plugin to manage these customizations.

Writing custom function plug-ins

I usually add a lot of code to my WordPress site that is used to add some special functionality rather than just changing the look of the site.

When I need to add some specific custom features to my website, I create something called a Custom Features plugin. For example, if my site is called 'WP Mayor', then I would create a plugin called 'WP Mayor Custom Features'.

It's important to give the plugin a good name because then other people who manage the site will know at a glance that the plugin is directly related to this site and that the plugin may only contain changes to this site.

Also, make sure that the plugin's name is unique so that it won't be confused with other plugins in the official WordPress plugin repository, and to avoid your plugin being overwritten by mistake.

Creating such a plugin is easy, just create a new folder in the wp-content/plugins directory, as you will probably need to add a lot of files, including some code files like JavaScript and CSS.

Using 'WP Mayor' as an example, we would then create a folder called 'wp-mayor-custom-functions' in the wp-content/plugins directory, and then inside that Create a main plugin file called 'wp-mayor-custom-functions.php'.

We need to write some code in this main file to tell WordPress that this is a plugin. While it's possible to get the plugin running by just filling in the plugin name, I'll show you a sample header that contains more information.

/**

* Plugin Name: WP Mayor Custom Function

* Plugin URI: https://wpmayor.com

* Description: All the cool features we custom-built for us.

* Version: 1.0.0

* Requires at least: 6.2

* Requires PHP: 8.1

* Author: Thomas Maier

*/

When you've completed the above steps, the plugin you created should appear in the "Plugins" section of your WordPress control panel. So you can see and manage it there.

Now we can start adding real PHP code to our files.

A tip: If I can't access the site with FTP, or if I'm just feeling lazy, I'll use a plugin called Pluginception to get a quick start. Then I can add more code directly in the plugin editor in the WordPress control panel.

You may ask, should I put all my custom code in a plugin? That really depends. If I know that some of the code will be used in many different projects, I'll put them in different plugins. However, code that is dedicated to a specific site, I put in the same plugin. That way I don't have to manage a lot of different codebases.

That sounds okay, right? However, from my experience managing a large plugin company and making many tweaks to websites, I've found that these custom plugins are still usually too developer-focused. Let's explore a different approach in the next section.

Use the code snippet plugin to manage

I keep all the generic code in a dedicated plugin so that I can stay organized. I also make sure that all changes and adjustments, such as special promotions or important updates, are clearly documented and organized in easy-to-understand files.

While the code was easy for me to understand, I realized that it might not be the most efficient way to do it, especially as more and more people need to manage websites.

In order to make it easy for everyone to understand and manage these customizations, I decided to use a WordPress plugin that allows us to manage all the code snippets directly in the WordPress control panel.

I especially like to use a free plugin called "Code Snippets". It adds a new section to the dashboard where all the code snippets are listed. Now anyone with administrative privileges can easily view and edit the code. I've also given each code snippet a descriptive name and used comments to detail what they do, as well as labels for different changes to make it easier to organize.

My tags are usually the name of the plugin or theme I'm tweaking and the part of the page it relates to, such as "WooCommerce" and "Checkout".

If you give the code and files easy-to-understand names and organize them well, then anyone, including myself, can easily find and understand the tweaks. I even use this method on my own personal website because it makes it easy for me.

Using a custom function plugin is perfect for code snippets that you only need to use temporarily, such as some cleanup that you have to run occasionally, or some front-end functionality that you only need at a specific time, like opening a promotion.

And is this method safe?

Typically, WordPress allows anyone with administrator privileges to edit a site's plugin and theme code. The same goes for using custom code plugins. So, the old rule: assign each person only the permissions they need so you can keep your site secure.

An important point for developers is that when you manage code through plugins, some code may need to be loaded before all other plugins. If your code requires this, you should consider using a special plugin type called "MU Plugins" so that your code can be loaded before other plugins.

Customize WordPress Features with Essential Plugins

Essential Plugins are special plugins that run before all other normal plugins in WordPress. I use them to control whether certain plugins are turned on or off on a particular page. This type of code can also help speed up specific functions, such as faking API calls or optimizing responsiveness in the backend.

An important feature is that these essential plugins are automatically turned on and cannot be turned off or modified in the WordPress control panel. This makes them perfect for hosting core code that shouldn't even be changed by administrators.

Creating the necessary plug-ins

Essential Plugins" is stored in the wp-content/mu-plugins directory in the WordPress folder. Usually, new installations of WordPress don't have this folder, but sometimes plugins or web hosting services may automatically add something to it.

If you want to add new plugins to this mu-plugins folder, you need to create a PHP file on your computer first, like the custom plugin I showed before. However, giving this file a unique name is not necessary here, as these essential plugins will not be automatically updated like other plugins.

When you are happy with your new plugin, you will need to manually upload it via FTP to the wp-content/mu-plugins folder. If this folder doesn't exist yet, you'll have to create a new one yourself.

While you can't modify these essential plugins through the WordPress admin interface, you can find them in the "Enforce Usage" section under the "Plugins" menu.

Ideally, essential plugins should be in a single file. While you can reference other files in a main PHP file, WordPress can't find those files stored in subfolders. If your essential plugin gets complicated, you should consider putting the main code into a common plugin and then only using the essential plugin to load and run all the code that must be executed before all the other plugins.
summarize

We've looked at several ways to add custom code to WordPress: from adding code to your theme's functions.php file, to creating standalone plugins and custom function plugins, to using essential plugins (mu-plugins). Each method has its own advantages and possible drawbacks for different situations. It depends on the type of changes you want to make and who needs to use them.

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