Now that you are on your way and ready to write whatever JavaScript you need for your application, and you are able to integrate this with the Drupal backend APIs, let's take a look at the Ajax framework. There's a lot we can do on the client side without having to write a single line of JavaScript code.
The Drupal Ajax API is a robust system that allows us to define client-side interactions via PHP. We most commonly use Ajax when we interact with forms—triggering certain actions that change the DOM without having to reload the page. We will demonstrate how all this works by expanding a bit more on the importer functionality we built in Chapter 7, Your Own Custom Entity and Plugin Types. Before, though, let's take a quick look at the simpler use case of Ajax in Drupal 8.