#### 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
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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

7.1. Sum as you will. The following exercise will help you understand some of the concepts we dealt with above, even if you solve it without using any of the functions we saw in the chapter. Write a `sumMany()` function that lets you sum an indeterminate quantity of numbers, in the following fashion. Note that when the function is called with no arguments, the sum is returned:

```     let result = sumMany((9)(2)(3)(1)(4)(3)());
// 22
```

7.2. Working stylishly. Write an `applyStyle()` function that will let you apply basic styling to strings, in the following way. Use either currying or partial application:

```     const makeBold = applyStyle("b");
document.getElementById("myCity").innerHTML =
makeBold("Montevideo");
// <b>Montevideo</b>, to produce
Montevideo

const makeUnderline = applyStyle("u");
document.getElementById("myCountry").innerHTML =
makeUnderline("Uruguay");
// <u>Uruguay</u>, to produce
Uruguay
```

7.3. Currying...