Overview of this book

Functional programming is a paradigm for developing software with better performance. It helps you write concise and testable code. To help you take your programming skills to the next level, this comprehensive book will assist you in harnessing the capabilities of functional programming with JavaScript and writing highly maintainable and testable web and server apps using functional JavaScript. This second edition is updated and improved to cover features such as transducers, lenses, prisms and various other concepts to help you write efficient programs. By focusing on functional programming, you’ll not only start to write but also to test pure functions, and reduce side effects. The book also specifically allows you to discover techniques for simplifying code and applying recursion for loopless coding. Gradually, you’ll understand how to achieve immutability, implement design patterns, and work with data types for your application, before going on to learn functional reactive programming to handle complex events in your app. Finally, the book will take you through the design patterns that are relevant to functional programming. By the end of this book, you’ll have developed your JavaScript skills and have gained knowledge of the essential functional programming techniques to program effectively.
Preface
Technical Requirements
Free Chapter
Becoming Functional - Several Questions
Thinking Functionally - A First Example
Starting Out with Functions - A Core Concept
Behaving Properly - Pure Functions
Programming Declaratively - A Better Style
Producing Functions - Higher-Order Functions
Transforming Functions - Currying and Partial Application
Connecting Functions - Pipelining and Composition
Designing Functions - Recursion
Ensuring Purity - Immutability
Implementing Design Patterns - The Functional Way
Building Better Containers - Functional Data Types
Bibliography
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Chapter 4, Behaving Properly – Pure Functions

4.1. Minimalistic function: It works because fib(0)=0 and fib(1)=1, so it's true that for n<2, fib(n)=n.

4.2. A cheap way: Basically, this algorithm works the same way as you'd calculate a Fibonacci number by hand. You'd start by writing down fib(0)=0 and fib(1)=1, adding them to get fib(2)=1, adding the last two to get fib(3)=2, and so on. In this version of the algorithm, a and b stand for two consecutive Fibonacci numbers. This implementation is quite efficient!

4.3. A shuffle test: Before shuffling the array, sort a copy of it, JSON.stringify() it, and save the result. After shuffling, sort a copy of the shuffled array and JSON.stringify() it as well. Finally, two JSON strings should be produced, which should be equal. This does away with all the other tests since it ensures that the array doesn&apos...