Table of Contents for
Beginning Functional JavaScript: Uncover the Concepts of Functional Programming with EcmaScript 8

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Beginning Functional JavaScript: Uncover the Concepts of Functional Programming with EcmaScript 8 by Srikanth Machiraju Published by Apress, 2018
  1. Navigation
  2. Cover
  3. Front Matter
  4. 1. Functional Programming in Simple Terms
  5. 2. Fundamentals of JavaScript Functions
  6. 3. Higher Order Functions
  7. 4. Closures and Higher Order Functions
  8. 5. Being Functional on Arrays
  9. 6. Currying and Partial Application
  10. 7. Composition and Pipelines
  11. 8. Fun with Functors
  12. 9. Monads in Depth
  13. 10. Pause, Resume, and Async with Generators
  14. 11. Building a React-Like Library
  15. 12. Testing and Closing Thoughts
  16. Back Matter
Anto Aravinth and Srikanth Machiraju
Beginning Functional JavaScriptUncover the Concepts of Functional Programming with EcmaScript 82nd ed.
Anto Aravinth
Chennai, Tamil Nadu, India
Srikanth Machiraju
Hyderabad, Andhra Pradesh, India
ISBN 978-1-4842-4086-1e-ISBN 978-1-4842-4087-8
https://doi.org/10.1007/978-1-4842-4087-8
Library of Congress Control Number: 2018964615
© Anto Aravinth, Srikanth Machiraju 2018
This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed.
Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, log os, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.
While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.
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Introduction

The second edition of a book is always special. When I wrote the first edition, I had about two years of IT experience. The book received positive as well as negative responses. I always wanted to work on the negative responses to make the content better and make the book worth the price. In the meantime, JavaScript evolved a great deal. Many ground-breaking changes were added into the language. The Web is full of JavaScript, and imagine a world without the Web. Hard, right?

This second edition is a much improved version that teaches the fundamentals of functional programming in JavaScript. We have added much new content in this second edition; for example, we will be building a library for building web applications using functional concepts, and we have added sections on testing as well. We have rewritten the book to match the latest ES8 syntax with many samples of async, await patterns, and a lot more!

We assure you that you will gain a lot of knowledge from this book and at the same time you will have fun while running the examples. Start reading.

Acknowledgments

I remember the first code that I wrote for Juspay Systems in my first job as an intern. Coding was fun for me; at times it is challenging, too. Now with six years of software experience, I want to make sure I pass on all the knowledge I have to the community. I love teaching people. I love to share my thoughts with the community to get feedback. That’s exactly the reason I’m writing a second edition of this book.

I have to acknowledge few people who have been standing right next to me in all phases of my life: my late father Belgin Rayen, mother Susila, Kishore (brother-in-law), Ramya (sibling), and Joshuwa (my new little nephew). They have been supportive and pushed me harder to achieve my goals. I want to say thanks to Divya and the technical reviewer of this book, as they did a wonderful job. Luckily, I have a wonderful coauthor in Srikanth, who did an amazing job as well.

Finally, I want to give special thanks to Bianaca, Deepak, Vishal, Arun, Vishwapriya, and Shabala, who have added joy to my life.

Please reach out to me at anto.aravinth.cse@gmail.com with any feedback.

—Anto Aravinth

I would like to thank Apress for providing me a second opportunity to author. I would also like to thank my family, especially my dear wife Sonia Madan and my four-month-old son Reyansh for supporting me throughout this stint. I’m always reachable at Vishwanath.srikanth@gmail.com for any feedback or questions.

—Srikanth Machiraju

Table of Contents

Chapter 1:​ Functional Programming in Simple Terms 1
What Is Functional Programming?​ Why Does It Matter?​ 2
Referential Transparency 5
Imperative, Declarative, Abstraction 7
Functional Programming Benefits 8
Pure Functions 8
Pure Functions Lead to Testable Code 9
Reasonable Code 11
Parallel Code 12
Cachable 14
Pipelines and Composable 16
A Pure Function Is a Mathematical Function 17
What We Are Going to Build 18
Is JavaScript a Functional Programming Language?​ 19
Summary 20
Chapter 2:​ Fundamentals of JavaScript Functions 21
ECMAScript:​ A Bit of History 22
Creating and Executing Functions 23
First Function 24
Strict Mode 26
Return Statement Is Optional 28
Multiple Statement Functions 28
Function Arguments 30
ES5 Functions Are Valid in ES6 and Above 30
Setting Up Our Project 30
Initial Setup 31
Our First Functional Approach to the Loop Problem 33
Gist on Exports 36
Gist on Imports 36
Running the Code Using Babel-Node 37
Creating Script in Npm 38
Running the Source Code from Git 39
Summary 40
Chapter 3:​ Higher Order Functions 41
Understanding Data 42
Understanding JavaScript Data Types 42
Storing a Function 43
Passing a Function 44
Returning a Function 45
Abstraction and Higher Order Functions 47
Abstraction Definitions 48
Abstraction via Higher Order Functions 48
Higher Order Functions in the Real World 53
every Function 53
some Function 55
sort Function 56
Summary 61
Chapter 4:​ Closures and Higher Order Functions 63
Understanding Closures 64
What Are Closures?​ 64
Remembering Where It Is Born 67
Revisiting sortBy Function 69
Higher Order Functions in the Real World (Continued) 70
tap Function 70
unary Function 72
once Function 74
memoize Function 75
assign function 78
Summary 80
Chapter 5:​ Being Functional on Arrays 81
Working Functionally on Arrays 82
map 82
filter 87
Chaining Operations 88
concatAll 90
Reducing Function 95
reduce Function 95
Zipping Arrays 102
zip Function 105
Summary 108
Chapter 6:​ Currying and Partial Application 109
A Few Notes on Terminology 110
Unary Function 110
Binary Function 110
Variadic Functions 110
Currying 112
Currying Use Cases 114
A logger Function:​ Using Currying 116
Revisit Curry 117
Back to logger Function 122
Currying in Action 123
Finding a Number in Array Contents 124
Squaring an Array 124
Data Flow 125
Partial Application 125
Implementing partial Function 127
Currying vs.​ Partial Application 130
Summary 130
Chapter 7:​ Composition and Pipelines 133
Composition in General Terms 134
Unix Philosophy 134
Functional Composition 137
Revisiting map,filter 137
compose Function 139
Playing with the compose Function 140
curry and partial to the Rescue 142
compose Many Functions 146
Pipelines and Sequence 148
Implementing pipe 149
Odds on Composition 150
The Pipeline Operator 151
Debugging Using the tap Function 154
Summary 155
Chapter 8:​ Fun with Functors 157
What Is a Functor?​ 158
Functor Is a Container 158
Implementing map 161
MayBe 163
Implementing MayBe 163
Simple Use Cases 165
Real-World Use Cases 168
Either Functor 173
Implementing Either 174
Reddit Example Either Version 176
Word of Caution:​ Pointed Functor 179
Summary 180
Chapter 9:​ Monads in Depth 181
Getting Reddit Comments for Our Search Query 182
The Problem 183
Implementation of the First Step 185
Merging Reddit Calls 189
Problem of Nested/​Many maps 194
Solving the Problem via join 196
join Implementation 196
chain Implementation 200
Summary 203
Chapter 10:​ Pause, Resume, and Async with Generators 205
Async Code and Its Problem 206
Callback Hell 206
Generators 101 209
Creating Generators 209
Caveats of Generators 210
yield Keyword 211
done Property of Generator 214
Passing Data to Generators 216
Using Generators to Handle Async Calls 219
Generators for Async:​ A Simple Case 219
Generators for Async:​ A Real-World Case 226
Async Functions in ECMAScript 2017 230
Promise 230
Await 231
Async 231
Chaining Callbacks 233
Error Handling in Async Calls 236
Async Functions Transpiled to Generators 237
Summary 239
Chapter 11:​ Building a React-Like Library 241
Immutability 242
Building a Simple Redux Library 245
Building a Framework Like HyperApp 251
Virtual DOM 252
JSX 254
JS Fiddle 255
CreateActions 261
Render 262
Patch 263
Update 264
Merge 265
Remove 266
Summary 268
Chapter 12:​ Testing and Closing Thoughts 269
Introduction 270
Types of Testing 272
BDD and TDD 273
JavaScript Test Frameworks 274
Testing Using Mocha 275
Mocking Using Sinon 283
Testing with Jasmine 287
Code Coverage 290
Linting 291
Unit Testing Library Code 294
Closing Thoughts 296
Summary 297
Index 299

About the Authors and About the Technical Reviewer

About the Authors

Anto Aravinth
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has been in the software industry for more than six years. He has developed many systems that are written in the latest technologies. Anto has knowledge of the fundamentals of JavaScript and how it works and has trained many people. Anto is also does OSS in his free time and loves to play table tennis.

 
Srikanth Machiraju
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has over ten years of experience as a developer, architect, technical trainer, and community speaker. He is currently working as Senior Consultant with Microsoft Hyderabad, leading a team of 100 developers and quality analysts developing an advanced cloud-based platform for a tech giant in the oil industry. With an aim to be an enterprise architect who can design hyperscale modern applications with intelligence, he constantly learns and shares modern application development tactics using cutting-edge platforms and technologies. Prior to Microsoft, he worked with BrainScale as Corporate Trainer and Senior Technical Analyst on application design, development, and migrations using Azure. He is a tech-savvy developer who is passionate about embracing new technologies and sharing his learning via blog and community engagements. He has also authored the “Learning Windows Server Containers” and “Developing Bots with Microsoft Bot Framework,” blogs at https://vishwanathsrikanth.wordpress.com . He runs his own YouTube channel called “Tech Talk with Sriks” and is active on LinkedIn at https://www.linkedin.com/in/vishsrik/ .

 

About the Technical Reviewer

Sakib Shaikh
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has been working as a Tech Lead with a large scientific publisher, with more than ten years of experience as a full stack developer with JavaScript technologies on front-end and back-end systems. He has been reviewing technical books and articles for the past few years and contributes to the developer community as a trainer, blogger, and mentor.