getify/functional-light-js

★ 16,768JavaScriptAudience · developerComplexity · 1/5DormantLicenseSetup · easy

Mindmap

mindmap
  root((Functional Light JS))
    Inputs
      Reader with JS skills
    Outputs
      11 chapters
      Code examples
      2 appendices
    Use Cases
      Learn FP basics
      Refactor toward pure functions
      Apply composition and immutability
    Topics
      Closures
      Recursion
      Composition
      Side effects
      Immutability

mindmap root((Functional Light JS)) Inputs Reader with JS skills Outputs 11 chapters Code examples 2 appendices Use Cases Learn FP basics Refactor toward pure functions Apply composition and immutability Topics Closures Recursion Composition Side effects Immutability

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Things people build with this

USE CASE 1

Learn functional programming basics as a working JavaScript developer

USE CASE 2

Refactor an existing codebase toward pure functions and immutability

USE CASE 3

Use the chapters as a study guide for a team book club

Tech stack

JavaScript

Getting it running

Difficulty · easy Time to first run · 5min

Reading material, not code to run, so the only setup is opening the markdown files on GitHub.

Creative Commons Attribution-NonCommercial-NoDerivs license, so you can read and share it freely but cannot remix or sell it.

In plain English

Functional-Light JavaScript is a free, online book about functional programming (FP) in JavaScript. Functional programming is a coding style that emphasizes writing code as pure, predictable functions with no hidden side effects, leading to programs that are easier to reason about and test. The book's stated goal is to make FP approachable for JavaScript developers without drowning them in academic jargon. The author calls the approach "Functional-Light Programming", it covers a practical subset of FP concepts rather than the full formal theory. The title's word "Light" refers to limited scope, not beginner level: the book goes deep into each topic and expects you to already know JavaScript reasonably well. Topics covered across eleven chapters include: why functional programming matters, how functions work at a deeper level, composing functions (building complex operations from simpler ones), managing side effects (unpredictable behavior that depends on things outside a function), value immutability (not changing data in place), closures, recursion, list operations, and asynchronous functional patterns. Two appendices cover transducing and monads, more advanced FP concepts. You would read this book if you are a JavaScript developer who has heard about functional programming and wants to start applying its ideas in real code, but finds purely theoretical or academic presentations off-putting. The book is available to read free on GitHub, and can also be purchased in ebook and print formats from Leanpub, Manning, and Amazon.

Copy-paste prompts

Prompt 1

Summarize the key takeaways of chapter 4 of Functional Light JS on composition with a fresh code example

Prompt 2

Refactor this imperative JavaScript loop into the pure functional style taught in Functional Light JS

Prompt 3

Compare Functional Light JS to a fully theoretical FP book and tell me what is intentionally left out

Prompt 4

Write 10 exercises a reader can do after finishing Functional Light JS to lock in the concepts

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