What Are Asset Libraries? for Drupal 8, 9, and 10

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.