This book presents detailed, step-by-step recipes, explanations and code examples for creating WordPress. Learn how to extend WordPress, how to use the WordPress plugin API, and how to mold WordPress to your project's needs.

WordPress Plugin Development Cookbook, Third Edition

One in five sites on the web today are powered by WordPress. It’s a huge ecosystem with themes, plugins, and a helpful and dedicated community.

WordPress

Plugins

Preface

Before you start writing your first WordPress plugin, it is important to have a good set of tools in place that will allow you to work locally on your computer and be more efficient in your work. While it is possible to perform some development tasks with the built-in tools that are provided with the operating system, creating a solid local development environment will help you develop plugins quickly and have full control over your server settings to be able to test different configurations.

Preparing a Local Development Environment

From its very first beginnings, WordPress has always been designed as a very open platform. This openness has been exemplified not only through its open source licensing and distribution model but also its open plugin architecture, providing developers with the ability to deliver an even richer experience to its users.

Plugin Framework Basics

As we saw in Chapter 2 , Plugin Framework Basics , it is very easy for a plugin to register custom functions with action and filter hooks to change or augment the way WordPress renders web pages. That being said, some of the examples covered in Chapter 2 , Plugin Framework Basics, have limitations when it comes to dealing with custom user information, such as the inability to easily specify a Google Analytics account number.

User Settings and Administration Pages

Building on its history of openness and ease of use, WordPress reached new heights in customization when it introduced custom post types.

The Power of Custom Post Types

In the last few chapters, you learned how to create configuration panels for your plugins and how to set up custom post types. With this knowledge in hand, we will now see how to customize the post and page editors using meta boxes.

Customizing Post and Page Editors

As mentioned a few times thus far, a large evolution in WordPress functionality came in version 5.0 with the introduction of the Block Editor , also well known by its development codename, Gutenberg . While the original page editor was quite functional and had been supporting content creators for many years, it did not provide full What You See Is What You Get ( WYSIWYG ) functionality. More specifically, users building a complex website were often required to use shortcodes that are only seen once a page is saved and viewed on the site, or even had to type in HTML code. Of course, many third-party plugins ( Visual Composer , WPBakery , Elementor , Divi , and so on) saw this as an opportunity to provide more advanced page building interfaces, eventually leading to the WordPress development team creating their own solution with the block editor.

Extending the Block Editor

Giving users the ability to contribute content to a website is always a good way to engage the community and keep content fresh on a website. That being said, WordPress does not provide any built-in mechanism for site visitors to submit content to site administrators. This is even more obvious when you consider that adding a simple contact form to a site requires the installation of a plugin.

Accepting User Content Submissions

After learning how to customize the post editor and taxonomies with custom data fields, the next areas that we will be augmenting are the user creation and editing sections of WordPress. This type of modification can be used for many different purposes, including tracking when users have last visited a site or storing additional data on the types of services they are interested in. This chapter expands on the private content plugin that we started in the Creating a new enclosing shortcode recipe in Chapter 2 , Plugin Framework Basics , and the Storing stylesheet data in user settings recipe in Chapter 3 , User Settings and Administration Pages . This time around, we are adding a second level of content protection that will restrict specially identified post or page content to only be displayed for paid users.

Customizing User Data

JavaScript libraries, especially the very popular jQuery library along with its numerous plugins, can do wonders in bringing a website to life with slick animations, dynamic data queries, and advanced graphical features. Unfortunately, for all of their benefits, these scripts can also be difficult to work with. For example, loading more than one copy of jQuery can destroy everything that was set up by another instance, and errors in one script usually prevent other scripts from running correctly.

Leveraging JavaScript, jQuery, and AJAX Scripts

Widgets have been present in WordPress from the early days of the platform. They allow users to easily populate sidebars or other widget areas of their website theme with content that is provided by WordPress itself (post or page data) or by any plugins that have been installed (for example, book review system information). Starting with the recent version 5.8, WordPress introduced the ability to use blocks from the block editor in the widget area. That being said, the platform continued supporting legacy widgets, coded using a combination of PHP and HTML. In the subsequent version 5.9, WordPress introduced the concept of block themes, with the first example theme not supporting widgets. We can therefore say that the future of widgets is a bit uncertain, but they are still relevant to the large majority of site themes out there today.

Adding New Widgets to the WordPress Library

After spending most of our time learning how to extend WordPress to allow site administrators and users to create local content, this chapter focuses on interacting with external data sources. While we did some work with displaying Twitter feed content in the Creating a new shortcode with parameters recipe in Chapter 2 , Plugin Framework Basics , we had very little control over how this data was displayed since the content was shown in an IFrame . We also had no control over how this data was fetched and no way to cache it. The reason for this is that every user loading a page containing the Twitter feed shortcode fetched their own copy of the information to be displayed.

Fetching, Caching, and Regularly Updating External Site Data

WordPress is a worldwide phenomenon, with users embracing the platform all around the globe. To create a more immersive experience for users in different locales, WordPress offers the ability to translate all of its administrator- and visitor-facing content. Like most other functionalities on the platform, internationalization is also available to plugin developers. By calling a set of easy-to-use functions, developers can include translation files with their creations.

Enabling Plugin Internationalization

Once you have a version of your new plugin that is ready to be distributed to the masses, you need to decide whether you will join the official WordPress repository or self-publish it.

WordPress Plugin Development Cookbook, Third Edition

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Yannick Lefebvre

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WordPress Plugin Development Cookbook, Third Edition