In computer programming, paradigms abound. Some examples include imperative programming, structured (goto-less) programming, object-oriented programming (OOP), aspect-oriented programming, and declarative programming. Lately, there has been renewed interest in a particular paradigm that can arguably be considered to be older than most (if not all) of the cited ones—Functional Programming (FP). FP emphasizes writing functions and connecting them in simple ways to produce a more understandable and more easily tested code. Thus, given the increased complexity of today's web applications, it's logical that a safer, cleaner way of programming would be of interest.
It must also be said that FP hasn't been generally applied in industry, possibly because it has a certain aura of difficulty, and it is thought to be theoretical rather than practical, even mathematical, and possibly uses vocabulary and concepts that are foreign to developers—for example, functors? Monads? Folding? Category theory? While learning all this theory will certainly be of help, it can also be argued that even with zero knowledge of the previous terms, you can understand the tenets of FP, and see how to apply it in your own programming.