At this point, it should come as no surprise that all modern web applications are inextricably tied to using JavaScript. There's no modern web without it, as interactions simply cannot happen in real time without it. The server side has its place and importance, but the crux of what the user sees and interacts with is controlled by JavaScript.
Just like CSS is a complement to HTML, JavaScript is the third friend in the group, creating meaningful experiences out of a collection of markup and styling. As the muscles of a web app, it provides us with rich interactions and logic, and is the foundation of all SPAs. It truly is a tool of wonder and beauty.
