JavaScript is used and loaded in special ways within a Drupal site. JavaScript is loaded via asset libraries and Drupal core provides a bunch of different JavaScript libraries that you can load and use in your module or theme. This tutorial provides a brief orientation to some of the JavaScript included in core.

In this tutorial we'll:

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.

New asset libraries can be defined by either modules or themes. In order to define a new asset library you need to create the requisite CSS and JavaScript files, and a new THEMENAME.libraries.yml, or MODULENAME.libraries.yml file that aggregates them together and provides metadata about the library itself and any dependencies.

In this tutorial we'll:

Once you've defined an asset library you'll need to tell Drupal when you want to add the CSS and JavaScript that it includes to the page. Ideally you'll do so in a way that allows Drupal to only add the corresponding assets on pages where they are needed.

Anyone writing JavaScript for Drupal should use the Drupal.behaviors API when writing their custom JavaScript functionality. Doing so ensures that your JavaScript is executed at the appropriate times during the life cycle of a page, such as when the page loads, or after new DOM elements have been added via an AJAX request.

In this tutorial we'll look at:

It's often useful to pass dynamically calculated values from the server to the client in order to make them available to your front-end JavaScript. Your JavaScript might need to know something particular about the user currently visiting the site or the value of a particular configuration variable. In this tutorial, we'll look at how Drupal can pass these values from the PHP code that executes during a page load to the front-end JavaScript in your theme.

In order to do this, we'll need to:

You may know that Drupal provides utility PHP functions for manipulating and sanitizing strings. Drupal also provides JavaScript functions for the same purpose. The two most useful are Drupal.checkPlain and Drupal.formatPlural. Drupal.checkPlain lets you ensure a string is safe for output into the DOM; it is useful when working with user-provided input. Drupal.formatPlural ensures that a string containing a count of items is pluralized correctly.

Sometimes your JavaScript needs to insert new strings into the user interface. In order to ensure that those user-facing strings can be translated into other languages, just like the rest of Drupal's user interface, you should make sure and use the Drupal.t function anytime you output a string of text.

Goal

Ensure that user-facing strings output from JavaScript running in Drupal are translatable.

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.

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:

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.

Goal

Install the ESLint application to verify your custom JavaScript files are meeting the Drupal coding standards.

It's probably not too surprising that a library called Backbone aims to provide structure to your front-end JavaScript code and applications. In this tutorial we'll take a look at how Backbone.js goes about achieving that goal, and how you can make use of it on your Drupal site. We'll first take a high-level look at the main components that make up the Backbone.js library. With that basic understanding in place we'll look at an example of how you might integrate Backbone.js into a Drupal site.

Underscore.js is a very small library which provides several utility functions and helpers to make working with JavaScript a little bit easier. In this tutorial we'll take a look at a part of the library, learn where the full library is documented, and see how we can make use of Underscore.js in a custom block on our Drupal site.

Goal

Learn about the Underscore.js library and how to use it in a Drupal site.

In developing the theme for your website it's important to take accessibility into account. Making your site available and functional for as many users as possible is always a good idea. Progressive enhancement and graceful degradation are key, but how do you go about accounting for the minute differences between browser capabilities? This is where the Modernizr.js library can help you out.