How to create self-populating “smart” forms in Drupal 8 with Form API

Hello! Many years ago (2015 to be exact), we published an article on how to create self-populating dropdown forms using the Drupal 7 Webform API. Now that the year is 2019 and Drupal 8 has been “Released” for quite some time now, with 8.7.1 as of May 2019, we thought it might be a good idea to update the strategy to do the same or similar action in Drupal 8. What are we trying to do anyways? Well we want a way for people to interact with a Webform in an interactive way. This means we want subsequent dropdown selections to be populated by previous choices. This logic doesn’t have to be restricted to dropdowns, it can be input  boxes, checkboxes or radio buttons. Anything, really. In the example above, you can see “Beverage” is chosen for “Industries”. The “Products” dropdown underneath has the options that you see  populated based […]