Actually, yes -- that's one of the topics I cover specifically in the course. Scala.js is a pretty major thing these days: that's Scala compiled to Javascript, which is a single-threaded environment. So there, you're programming *asynchronously*, but not *concurrently* -- which, frankly, makes it much easier than life on the JVM.

As I say in the course, you should be focused on programming asynchronously, which is really helpful and generally pretty easy. Concurrency makes things run much *faster*, but introduces scads of headaches in the process -- much of the course is about various ways to tame those headaches, such as immutable data structures, functional programming and Akka...