In Drupal, whenever we output markup it's best practice to use a Twig template or a theme function. But whenever you need to output DOM elements within JavaScript the best practice is to use the Drupal.theme function. This function ensures that the output can be overridden just like the HTML output by Twig. This tutorial covers how to use the Drupal.theme function in your JavaScript when inserting DOM elements, as well as how to replace the markup output by other JavaScript code that is using the Drupal.theme function.

ESLint is the linting tool of choice for JavaScript in Drupal. In this tutorial we’ll show how to install the ESLint application and then use it to verify that your JavaScript files are meeting the Drupal coding standards.

Drupal (as of version 8.4) has adopted the Airbnb JavaScript coding standards. In this tutorial, we'll walk through how to install the necessary package dependencies to run eslint on JavaScript files within your Drupal site.

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.

Template files are responsible for the HTML markup of every page generated by Drupal. Any file ending with the .html.twig extension is a template file. These files are composed of standard HTML markup as well as tokens used by the Twig template engine to represent dynamic content that will be substituted into the HTML markup when the template is used. As a theme developer, you'll work with this a lot.

In this tutorial we’re going to learn about:

• What template files are, and how they fit into the big picture of creating a theme
• How template files are used in order to allow theme developers to modify the HTML markup output by Drupal
• Naming conventions for, and specificity of, template files

Themes are the part of Drupal that you, and anyone else visiting your Drupal powered application, see when they view any page in their browser. You can think of a theme as a layer, kind of like a screen, that exists between your Drupal content and the users of your site. Whenever a page is requested Drupal does the work of assembling the content to display into structured data which is then handed off to the presentation layer to determine how to visually represent the data provided.

Drupal themes are created by front-end developer. Frequently referred to as themers, or theme developers. Themes consist of standard web assets like CSS, JavaScript, and images, combined with Drupal-specific templates for generating HTML markup, and YAML files for telling Drupal about the file and features that make up each individual theme.

In this tutorial we'll:

• Explain what a Drupal theme is.
• Explain the role of a Drupal themer in the process of building a Drupal site.
• Get a high level overview of the types of files/code that themes are made of.

By the end of this tutorial you should be able to explain what a Drupal theme is, and the kind of work a Drupal theme developer will be expected to do.

Maybe you've heard of anonymous closures but you're not quite sure how they apply in Drupal, or why using them is considered a best-practice. Anonymous closures allow you to avoid accidentally clashing with anything in the global scope, as well as to alias the jQuery object to the more commonly used $. This is necessary because Drupal runs jQuery in no-conflict mode. This tutorial will look at the syntax used for placing your custom JavaScript code inside an anonymous closure, and why it's a good idea to do so.

In this tutorial we'll:

• Explain what a closure is (briefly), and what immediately invoked function expressions are
• Show how typically Drupal JavaScript gets wrapped in a closure
• Provide a copy/paste example you can use in your own code

By the end of this tutorial you should be able to explain what an anonymous closure is, and how to use one in your custom JavaScript for Drupal.

The Drupal Console is a suite of tools run from a command line interface (CLI) to generate boilerplate code and interact with a Drupal installation.

Note: This project is no longer actively maintained. See the Drush topic for alternative solutions.

In this tutorial, we'll walk through the process of adding and configuring filters and adding a filter group.

In this tutorial, we'll walk through the process of adding and configuring sort criteria to a view.

In this tutorial, we'll add and configure a contextual filter for a view. Our Baseball Awards content type has a field Year. We'll make it possible for a page to be dynamically created on our site that contains the year and lists the awards for that specific year. To do this, we'll add a contextual filter to the Baseball Awards view that will allow visitors to filter the list of awards by the award year. We'll also add a block using the summary view contextual filter configuration, which visitors can use to view results for specific years.

One of the ways you can create a REST endpoint in Drupal is by using Views. In this tutorial, we'll add a REST endpoint display to a view of baseball players. We'll examine and configure settings that are unique to the REST endpoint display.

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

• Add a REST endpoint display to a view
• Understand how to configure settings for an endpoint

Instead of providing multiple views with different filter criteria, consider empowering your users by exposing filter criteria as an interactive form. You can even configure the forms to use AJAX to refresh results. In this tutorial, we'll walk through the process of adding and configuring exposed filter or sort criteria in a view.

Like exposed filters, we can expose sort criteria to the site visitor. Exposing sort criteria gives the visitor more control over the list of content they are viewing. In this tutorial, we'll configure our view of baseball players to allow visitors to sort the list in different ways by adding several exposed sort criteria.

Contextual filters are a Views mechanism for dynamically refining the contents of a view. It might be helpful to think of them as "dynamic filters". In this tutorial, we'll discuss the concept of context, look at how to add contextual filters in the Views UI, and review the Taxonomy term view that comes with Drupal and how it uses a contextual filter.

Exposing filter criteria allows the users of your site to choose how to filter a content list created in Views. When rendered on the page, the exposed filters will be displayed to the user as interactive form components.

By the end of this tutorial you will:

• Understand what it means to expose filter criteria and when it might be useful.
• Be able to identify when a view has exposed filters and which filters are exposed.

Exposing sort criteria allows the users of your site to sort a view using an interactive form.

By the end of this tutorial you will:

• Understand what it means to expose sort criteria and when it might be useful.
• Be able to identify a view's exposed sort criteria.

With filters, we can define query conditions and refine the results of a view. But what is a filter and how do filters work in Views? In this tutorial, you'll learn:

• How to add and configure filter criteria to a view to refine results
• What configuration options are available for filter criteria operators
• How filter groups allow you to group and order filter criteria to achieve desired results

By the end of this lesson, you should understand how to use and configure filter criteria in Views to refine the results of your view. (Note: We'll cover exposed filters in Overview: Exposed Filter Criteria in Views)

In order to display values for referenced entities in views, you need to add a relationship. What is a relationship, how do they work, and what does it mean to require this relationship? What are some common use cases for adding a relationship to a view? By the end of this tutorial you should be able to:

• Explain some common use cases for adding a relationship to a view.
• Understand the concept of entity references and how those field values can be displayed in a view.

With sort criteria, we can specify how to order our list. We can specify sort criteria using any field on or related to our view's base entity, and then specify in which order to sort, e.g. ascending or descending. If you are familiar with MySQL, it may be helpful to know that sort criteria are the ORDER BY clause of the query that Views builds. In this tutorial, you'll learn:

• How to add and configure sort criteria to a view to sort the list in various ways
• What configuration options are available

By the end of this lesson, you should understand how to use and configure sort criteria in Views. (Note: We'll cover exposed sort criteria in Overview: Exposed Sort Criteria in Views)