Refactoring JavaScript: Turning Bad Code Into Good Code

If your JavaScript is a mess, frameworks can only do so much to help. No matter what framework, "compiles-to-JS" language, or library you use, bugs and performance concerns will always be an issue if the underlying quality of your JavaScript is poor. With this hands-on guide, you’ll learn how test and refactor your existing code to help reduce complexity, improve readability, and gain confidence in the codebase.

Author Evan Burchard shows you how to identify areas of bad code, and then takes you through several refactoring methods for improving them. Techniques range from renaming variables to applying principles of functional and object-oriented programming. If you’re motivated to write better JavaScript code either on the frontend or backend, this book is a must.

• Use refactoring to restructure existing code, without changing its behavior
• Learn the relationship between refactoring and quality
• Explore the many versions of JavaScript in use today
• Create automated tests to confirm that your code works, and find bugs that slip through
• Learn how to refactor simple JavaScript structures, functions, and objects
• Refactor your codebase by applying object-oriented and functional programming principles
• Examine methods for refactoring asynchronous JavaScript

Table of Content

Chapter 1What Is Refactoring?

How Can You Guarantee Behavior Doesn’tChange?

What Is the Point of Refactoring if BehaviorDoesn’t Change?

What Is and Isn’t Refactoring

Wrapping Up

Chapter 2Which JavaScript Are You Using?

Versions and Specifications

Platforms and Implementations

Precompiled Languages

Frameworks

Libraries

What JavaScript Do You Need?

What JavaScript Are We Using?

Wrapping Up

Chapter 3Testing

The Many Whys of Testing

The Many Ways of Testing

Tools and Processes

Wrapping Up

Chapter 4Testing in Action

New Code from Scratch

New Code from Scratch with TDD

Untested Code and Characterization Tests

Debugging and Regression Tests

Wrapping Up

Chapter 5Basic Refactoring Goals

Function Bulk

Inputs

Outputs

Side Effects

Context Part 1: The Implicit Input

Context Part 2: Privacy

Wrapping Up

Chapter 6Refactoring Simple Structures

The Code

Our Strategy for Confidence

Renaming Things

Useless Code

Variables

Strings

Working with Arrays: Loops, forEach, map

Wrapping Up

Chapter 7Refactoring Functions and Objects

The Code (Improved)

Array and Object Alternatives

Testing What We Have

Extracting Functions

Streamlining the API with One Global Object

Wrapping Up

Chapter 8Refactoring Within a Hierarchy

About “CRUD Apps” and Frameworks

Let’s Build a Hierarchy

Let’s Wreck Our Hierarchy

Inheritance and Architecture

Has-A Relationships

Inheritance Antipatterns

Wrapping Up

Chapter 9Refactoring to OOP Patterns

Template Method

Strategy

State

null Object

Wrapper (Decorator and Adapter)

Facade

Wrapping Up

Chapter 10Asynchronous Refactoring

Why Async?

Fixing the Pyramid of Doom

Callbacks and Testing

Promises

Wrapping Up

Chapter 11Functional Refactoring

The Restrictions and Benefits of FunctionalProgramming

The Basics

Advanced Basics

Burritos

Learning and Using Burritos

Moving from OOP to FP

Wrapping Up

Chapter 12Conclusion

Appendix Further Reading and Resources

Origins of Refactoring

Baseline JavaScript(s)

Keeping Up with JavaScript

JavaScript Reference

Object-Oriented Programs/Patterns (IncludingAnticlass Stances)

Async

Functional

Tools

Non-JS-Specific but Relevant Sources

Me