Mastering WordPress Development: A Comprehensive Guide

The journey to becoming a skilled developer is challenging and continuous. New frameworks and web technologies constantly push developers to learn more each year. WordPress is one of the most popular PHP CMS platforms and powers almost 20% of all self-hosted websites.

If you’re into PHP development, WordPress is a system worth learning and mastering. But how do you go about doing so?

In this post, I’ll outline key areas of WordPress that every developer should understand. You may consider creating your own structured WordPress learning curriculum, where you focus on specific areas for a few weeks or months at a time. This will help you maintain focus and progress through WordPress at a steady pace.

Modern WordPress Theming

If you’re new to WordPress, it’s worth learning about the dashboard before diving into the nitty-gritty.

But I’m assuming you already know the basics and want to understand how to build on top of the WordPress platform with code.

Theming is the best place to start. Plugins are great, and custom functions are useful, but theming is essential for every WordPress site. Whether creating a new theme from scratch or customizing an existing one, you should be comfortable with WordPress’s theming system.

The only required files for a theme are the style.css stylesheet and the main index.php. WordPress theming uses conditional files, so if there isn’t a homepage.php, WordPress defaults to index.php. Similarly, if there’s no author.php for the author archive page, WordPress uses archive.php instead.

WordPress theming is straightforward once you learn the hierarchy. Here are the minimum bare-bones files that every WordPress theme should include:

• style.css – the theme’s official stylesheet with theme info
• index.php – fallback page for anything without a unique theme file
• home.php – your blog’s homepage, static or archive content
• single.php – a single post/article layout
• page.php – a single page layout
• archive.php – a catch-all for archives like categories, tags, authors, and dates
• 404.php – the default 404 error page layout

Advanced themes should include more specific files to define content and layout design better.

To learn more, check out the template files list in WordPress’s official documentation. There’s also a handy diagram explaining how theme file hierarchies operate:

Each theme is usually developed as a standalone entity that can include theme-dependent plugins and functions. All themes are written in PHP, allowing for a theme file to function as a library, restricting features to a single theme.

Alternatively, child theming can work well for building on top of an existing theme. This is an advanced topic, and not everyone likes child themes as they can get complicated quickly.

It’s worth understanding how they work and deciding if child themes fit a specific project.

Basic Plugin Development

The two key aspects of WordPress development are themes and plugins. Since themes affect the site’s layout and interface, they should be your first area of study. The natural next step is plugin development.

Building a WordPress plugin is challenging but manageable with practice. There’s enough online material to make it easier to learn.

It’s also possible to build WordPress websites entirely with free third-party plugins without writing your own. But skilled WordPress developers should understand how plugins function and how to write one when needed.

Two important terms you should know are filters and actions. Both take in code and return or output something, but in different ways.

Filters return code, such as a string of HTML or a newly updated variable. Actions output code directly into hooks predefined in WordPress themes, plugins, or even the WordPress core.

Check out this Stack thread to learn more.

These methodologies have functions that mirror each other. For example, add_action() and add_filter() work similarly for actions and filters, respectively. The same applies to do_action() and apply_filters().

Plugin development requires reading and practice. Confusion is part of the learning curve.

I recommend this Tuts+ guide covering the basics of actions and filters. WP Engineer also has a great post on defining your own hooks for building fully functional themes/plugins that can be extended with code.

Developing Internal Features

WordPress offers several internal features via classes and APIs that all developers can access. Some are advanced, like the rewrite API or the REST API, but beginners should start with simpler features:

Functions.php File

Opinions vary on the functions.php file. I’m a big fan. This file stores theme-specific functions and settings that define how the theme operates through shortcodes, hooks, and filters.

Your theme’s functions file can also have custom PHP functions called from other theme files. Some consider this bad practice, but it’s an effective way to organize theme-specific functions into one library.

Check out this list of free snippets to explore what’s possible with a theme’s functions.php file.

Shortcodes

Shortcodes are defined in PHP but can be added directly to content. They typically appear as square brackets in the WordPress post/page editor, like to build an image gallery.

Check out the shortcodes documentation for examples and to learn how they work.

Custom Post Types

Before WordPress 3.0, there were only a few default post types: attachments, posts, and pages. These are often enough for most WordPress websites.

But the introduction of CPTs allows developers to create new types like newsletters, eCommerce products, and user-submitted content.

These custom post types can also have their own custom taxonomies beyond the default tags and categories. CPTs can be defined via plugin or in a theme’s functions.php. There’s much flexibility once you learn how these work and how to write your own.

Custom Fields

Few developers understand the power of custom fields until they start using them. When writing a new post in the admin panel, you’ll notice widgets for tags, categories, a featured image, etc.

Custom fields add more widgets to the page for extra content, known as meta-data. The SEO plugin Yoast does this by adding its own custom fields in the post/page section to update the title/meta content.

It’s possible to add a field that stores any type of metadata, from multiple featured images to alternate author bios. The capabilities are limitless once you learn how to build custom fields and use the info effectively.

Advanced WordPress Development & Beyond

The content covered so far might take years to master and fully apply to your workflow. WordPress is easy to start with, but challenging to master.

Beyond theme and plugin development, consider incorporating specific WordPress APIs into your learning path. These are for advanced developers who want to explore everything WordPress offers.

Here are a few ideas to get you started:

• Settings API – define custom settings pages and input fields
• Options API – the standard method of storing database content
• Rewrite API – rewrite URLs and create custom WordPress permalinks
• Transients API – store temporary data in a database cache
• WP_Query – a class for writing custom database queries
• Walker – a class for managing tree data structures like page hierarchies

Remember that learning is an ongoing process. To become a skilled developer, you need consistent effort and passion for the industry.

Bookmark these topics and practice regularly, and you’ll find yourself among the ranks of many professional WordPress developers.