#### Overview of this book

Functional programming is a programming paradigm for developing software using functions. Learning to use functional programming is a good way to write more concise code, with greater concurrency and performance. The JavaScript language is particularly suited to functional programming. This book provides comprehensive coverage of the major topics in functional programming with JavaScript to produce shorter, clearer, and testable programs. You’ll delve into functional programming; including writing and testing pure functions, reducing side-effects, and other features to make your applications functional in nature. Specifically, we’ll explore techniques to simplify coding, apply recursion for loopless coding, learn ways to achieve immutability, implement design patterns, and work with data types. By the end of this book, you’ll have developed the JavaScript skills you need to program functional applications with confidence.
Dedication
Title Page
Credits
www.PacktPub.com
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Preface
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

## Questions

4.1. Minimalistic function: Functional programmers sometimes tend to write code in a minimalistic way. Can you examine this 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? Suggestion: try to calculate `fib4(6)` by hand, and compare 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 problems. Some basic mathematics properties are: a number should equal itself: for any number a, a should equal a

• If a number a equals number b, then b should...