Functional Programming in JavaScript

Last week I was really surprised to find Functional JavaScript: Introducing Functional Programming with Underscore.js by Michael Fogus in the local library and I just finished it and wanted to leave a short review here.

This book really delivers what the title promises: an introduction to functional programming in JavaScript using the library Underscore.js. It doesn't teach you JavaScript nor Underscore.js but teaches what the different functional programming concepts are and how they can be implemented in JavaScript. This is done in less then 250 pages of densely, in a good way, written text and example code. Starting from the basics like first-class functions, applicative programming, variable scoping and closures, the book moves on to higher-order functions, currying and partial function application. Then some side steps are made with a great chapter on recursion which ends with the trampoline and  a chapter on other important functional aspects like purity and immutability. Next is a chapter about flow-based programming, what it is, why it matters and different ways to define flows in your programs. The last chapter makes the connection with object-oriented programming and introduces mixins.

I really enjoyed reading this book because it is written very fluently without heavy (unnecessary) jargon and probably at a sweet spot on my learning curve. I've already read Real World Functional Programming: With Examples in F# and C# by Thomas Petricek and Jon Skeet and the first chapters of SICP but I haven't used it a lot in the wild. I've written my share of JavaScript programs but nothing very advanced, except maybe a Google Maps like library from scratch. If you're new to JavaScript AND functional programming then would advice against this book but otherwise, if you're motivated and don't let you get scared away by the first chapters then everything will be fine. But some playing around with the examples (like I did in this fiddle) and learning the basics of how to call passed in functions and how the often used Underscore.js functions (map, reduce, ...) work might be needed to get the most of this book. Overall this book is a very complete introduction to functional programming, the only thing I missed was a part on functional pattern matching. Note that this book is more about what introducing different functional programming techniques then about when and how to apply this techniques in your day-to-day programming.

Other books you might be interested in:
JavaScript: The Good Parts by Douglas Crockford (he popularized JSON and wrote JSLint and JSMin)
JavaScript: The Definitive Guide by David Flanagan
JavaScript Allongé by Reginald Braithwaite
Real World Functional Programming: With Examples in F# and C# by Thomas Petricek and Jon Skeet
Learn you a Haskell for Great Good! by Miran Lipovača
Learn you some Erlang for Great Good! by Fred Hébert