#### 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
Other Books You May Enjoy

# Questions

4.1. Minimalistic function: Functional programmers sometimes tend to write code in a minimalistic way. Can you examine the following version of the Fibonacci function and explain whether it works, and if so, how?

`const fib2 = n => (n < 2 ? n : fib2(n - 2) + fib2(n - 1));`

4.2. A cheap way: The following version of the Fibonacci function is quite efficient and doesn't do any unnecessary or repeated computations. Can you see how? Here's a suggestion: try to calculate fib4(6) by hand and compare it with the example given earlier in the book:

`const fib4 = (n, a = 0, b = 1) => (n === 0 ? a : fib4(n - 1, b, a + b));`

4.3. A shuffle test: How would you write unit tests for shuffle() to test whether it works correctly with arrays with repeated values?

4.4. Breaking laws: Using toBeCloseTo() is very practical, but it can cause some...