The most common use of Ajax in Drupal is through the Form API, where we can create dynamic interactions between the server and client with ease. To demonstrate how this works, we will go through an example. This will be a rework of the Importer configuration entity form we created in Chapter 7, Your Own Custom Entity and Plugin Types.
If you remember, we said that tying certain configuration values to the generic entity does not make sense, as importer plugins might be different. The first Importer we wrote loads a JSON file from a remote URL. So, it stands to reason that the configuration value for the URL is tied to the plugin and not the configuration entity (even if the latter actually stores it). Because if we want to create ...
