So why is Visualforce still a consideration? Lightning Framework has, over the years, become a rich and rounded programming framework in terms of reusable components and developer tooling. In its latest incarnation, known as Lightning Web Components, it has aligned even more closely with ubiquitous programming skills and standards that you may already be familiar with, such as W3C Web Components (https://github.com/w3c/webcomponents/).

If you're reading this book having already developed a Lightning (or Force.com as it was previously known) application prior to the advent of the Lightning Framework programming model, you will still very much be interested in leveraging Visualforce until you can migrate. In this case, you will also no doubt be interested in ways to combine both technologies. So you can perhaps start to develop new features in Lightning Framework.