I am new to Drupal, and I am trying to add some behavior to an existing page within Drupal.
Using the admin UI, I created an model with 2 numbers (num1, num2). I then rendered it into a form.
Now I would like to add a third field, and compute using the client the sum of num1 and num2 into this new field. This needs to be done as you type the numbers.
Then, I just add these to fields into a page like so:
I could really use some step by step examples, to just to know where to place a module, and what code to type in the module to only add this behavior to my content.
I am very new to Drupal, and I am using Drupal 8.