An asset library is a bundle of CSS and/or JavaScript files that work together to provide a style and functionality for a specific component. They are frequently used to isolate the functionality and styling of a specific component, like the tabs displayed at the top of each node, into a reusable library. If you want to include CSS and/or JavaScript in your Drupal theme or module you'll need to declare an asset library that tells Drupal about the existence, and location, of those files. And then attach that library to a page, or specific element, so that it gets loaded when needed.

In this tutorial we’ll:

• Define what an asset library is.
• Explain why asset libraries are used to include JavaScript and CSS files.
• Look at some example asset library definitions.

By the end of this tutorial you should be able to define what asset libraries are, and when you'll need to create one.

Preprocess functions allow Drupal themes to manipulate the variables that are used in Twig template files by using PHP functions to preprocess data before it is exposed to each template. All of the dynamic content available to theme developers within a Twig template file is exposed through a preprocess function. Understanding how preprocess functions work, and the role they play, is important for both module developers and theme developers.

In this tutorial we'll learn:

• What preprocess functions are and how they work
• The use case for preprocess functions
• The order of execution for preprocess functions

By the end of this tutorial you should be able to explain what preprocess functions are and the role they play in a Drupal theme.

As a developer, within a module, you can define settings for the module and provide a configuration form for administrators to update the values of those settings. In this tutorial, we'll create a configuration settings form for a module and define default values for each setting. We'll use Drupal Console, a command-line utility for Drupal to do some code scaffolding and speed up the process.

By the end of this lesson, you should be able to get a basic settings form up and running inside a custom module complete with default settings and a menu link.

Before we start synchronizing configuration, let's take a look at the default, out-of-the-box file location for staging and synchronizing configuration. Then we'll walk through how to change that directory to a location outside our project's docroot and update settings.php appropriately.

In this tutorial, we'll cover:

• The default location of the configuration sync directory
• How the configuration sync directory is secured
• How to change the location of the sync directory

The configuration system in Drupal was designed to manage and sync configuration between instances of a Drupal site. So before configuration management can be useful, we must have another instance—or clone—of our Drupal site. In this lesson, you will learn:

• Why cloning a Drupal site is necessary in order to manage configuration
• How to clone a Drupal site using tools that have a graphical user interface (GUI)

If you prefer using web-based or GUI tools rather than command line tools such as Drush and Git, then this lesson is for you.

Not every environment or copy of a site you may be working on will be created equally. You may want to enable logging on a development site or need to use different API keys depending on the environment. But you also need to make sure that your instance-specific configuration overrides don't make it into the database, mistakenly get exported, or compromise security.

In this tutorial, you will learn how to:

• Override the global $config array in settings.php (or settings.local.php)
• Retrieve overridden (immutable) configuration (read-only mode)
• Retrieve original (mutable) configuration for updating (read/write mode)
• Set dynamic values for configuration instead of overriding values

When you create a module for Drupal, it can be useful to provide default configuration. This can be settings for a form, the placement of a block, or something more complex like the default image styles provided by the Image module in core. A module can provide default configuration for simple configuration or configuration entities.

In this tutorial, we will cover:

• Possible locations for default configuration
• What happens with configuration when a module is installed or uninstalled
• Managing dependencies in configuration
• Where to find examples of default configuration

Configuration entities are suitable for creating user-defined configuration, such as image styles, views, content types, etc. A configuration entity type is defined by a module, default configuration is provided by that module as well as any other module, and then users can create zero or more configuration entities through Drupal's administrative UI.

In this tutorial, you will learn about:

• What configuration entities are
• Configuration entity types versus configuration entities
• An example in core: image style
• Overview of the process of creating your own configuration entity types in a module

In this tutorial, we'll cover how to load configuration entity data in a module. We'll change the AdminSettingsForm.php we created and replace the simple textfield we were using with a dropdown select list. Then we'll use data from our Transcode Profile module's configuration entity, loaded by the EntityTypeManager via the services container, to choose our preferred Transcode Profile.

By the end of this tutorial, you should be able to:

• Know how to load configuration entities using EntityTypeManager via the services container
• Update the AdminSettingsForm.php to use a dropdown select list
• Save your preferred transcode profile from a list of transcode profile entities
• Update the default configuration provided with the demo module to include transcode profiles