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Functional-Light JavaScript

License: CC BY-NC-ND 4.0

Book Cover

This book is a balanced, pragmatic look at FP in JavaScript. The first edition is now complete. Read here online for free, or:

Buy on Leanpub Buy on Manning Buy on Amazon

"Functional-Light JavaScript" explores the core principles of functional programming (FP) as they are applied to JavaScript. But what makes this book different is that we approach these principles without drowning in all the heavy terminology. We look at a subset of FP foundational concepts that I call "Functional-Light Programming" (FLP) and apply it to JavaScript.

Note: Despite the word "Light" in the title, I do not consider or recommend this book as a "beginner", "easy", or "intro" book on the topic. This book is rigorous and full of gritty detail; it expects a solid foundation of JS knowledge before diving in. "Light" means limited in scope; instead of being more broad, this book goes much deeper into each topic than you typically find in other FP-JavaScript books.

Let's face it: unless you're already a member of the FP cool kids club (I'm not!), a statement like, "a monad is just a monoid in the category of endofunctors", just doesn't mean anything useful to us.

That's not to say the terms are meaningless or that FPrs are bad for using them. Once you graduate from Functional-Light, you'll maybe/hopefully want to study FP more formally, and you'll certainly have plenty of exposure to what they mean and why.

But I want you to be able to apply some of the fundamentals of FP to your JavaScript now, because I believe it will help you write better, more reasonable code.

To read more about the motivations and perspective behind this book, check out the Preface.

Premium Sponsor


A big shoutout and thanks to Hiberly for being a premium sponsor of the Functional-Light JS book!

Their tool prioritises tech debt by grabbing feedback from developers after each merge. You can then draw cool graphs of your code versus happiness / frustration to help explain the impact of refactoring.

Check them out!


Table of Contents


This book has been published and is now available for purchase (in both ebook and print formats) from these sources:

Buy on Leanpub Buy on Manning Buy on Amazon

If you'd like additionally to contribute financially towards the effort (or any of my other OSS work) aside from purchasing the book, I do have a patreon that I would always appreciate your generosity towards.


In-person Training

The content for this book derives heavily from a training workshop I teach professionally (in both public and private-corporate workshop format) of the same name.

If you like this content and would like to contact me regarding conducting training on this, or other various JS/HTML5/Node.js topics, please reach out to me through email: getify @ gmail

Online Video Training

I also have several JS training courses available in on-demand video format. I teach courses through Frontend Masters, like my Functional-Light JavaScript v2 workshop. Some of my courses are also available on PluralSight.


Any contributions you make to this effort are of course greatly appreciated.

But PLEASE read the Contributions Guidelines carefully before submitting a PR.

License & Copyright

The materials herein are all (c) 2016-2018 Kyle Simpson.

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 Unported License.

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