One of the most fundamental aspects of modern computer programming is writing a program that interacts with servers. JavaScript is primarily a front-end language, meaning that it usually deals with the interactions with the user. There is usually some database or other remote service somewhere where your data is stored, retrieved, or manipulated from. So how do you access these services?
Many if not most modern services are accessed via HTTP/HTTPS requests on the Web (go back to Chapter 3 to ...