Book Image

Mastering JavaScript Functional Programming

By : Federico Kereki
Book Image

Mastering JavaScript Functional Programming

By: Federico Kereki

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.
Table of Contents (22 chapters)
Title Page
About the Author
About the Reviewer
Customer Feedback
Connecting Functions - Pipelining and Composition
Answers to Questions

Pure functions

Pure functions behave in the same way as mathematical functions and provide diverse benefits. A function may be considered to be pure if it satisfies two conditions:

  • Given the same arguments, the function always calculates and returns the same result, no matter how many times it's invoked, or in which conditions you call it. This result value cannot depend on any outside information or state, which could change during the program execution, and cause it to return a different value. Nor can the function result depend on I/O results, random numbers, or some other external variable, not directly controllable, value.
  • When calculating its result, the function doesn't cause any observable side effect , including output to I/O devices, mutation of objects, change to program state outside of the function, and so on.

If you want, you can simply say that pure functions don't depend on, and don't modify, anything outside its scope, and do always return the same result for the same input...