Drupal 8 Module Development - Second Edition

Altering forms

Before going ahead with our proposed functionality, I would like to open a parenthesis and discuss forms in a bit more detail. An important thing that you will do as a module developer is alter forms defined by other modules or Drupal core. So, it behooves us to talk about it early on and what better moment than now, when defining the form itself is still fresh in our minds.

Obviously, the form we just created belongs to us and we can change it however we want. However, many forms out there have been defined by other modules and there will be just as many times that you will want to make changes to them. Drupal provides us with a very flexible, albeit still procedural way of doing so—a suite of alter hooks; but what are alter ...