Define an Asset Library for Drupal 8, 9, and 10

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:

  • Look at the structure of a *.libraries.yml file and demonstrate how to combine a couple of CSS and JS files together into an asset library that can be used in a theme or a module
  • Look at how one asset library can declare that it is dependent on another in order to ensure the assets from the dependency are loaded as well

By the end of this tutorial you should know how to define a new asset library in either a module or a theme.