Refactoring JavaScript

Foreword

I still remember reading Martin Fowler’s book Refactoring: Improving the Design of Existing Code when it came out in 1999. It was a revelation: I had never before seen code being considered to be something malleable. Programmers tend to have the urge to rewrite code bases from scratch, but this book argued that it is possible to evolve and clean up existing code via small, principled, and comparatively safe steps. While doing so, tests provide an additional safety net and enable you to move forward with confidence. One piece of advice from the book will always stick with me—whenever you code, always keep two kinds of activity completely separate: implementing new functionality and refactoring existing code. If you do that, you’ll avoid doing too many things at the same time and will produce less bugs.

Refactoring JavaScript takes the ideas of refactoring and applies them to the world of JavaScript. JavaScript’s dynamic nature means that you need different techniques compared to more static languages such as Java. In Java, you have static typing. And inheritance and polymorphism are used quite often. For JavaScript, you often rely on static checking tools (such as ESLint and Flow) and can adapt objects flexibly according to your needs. Functional programming techniques are also more popular. Additionally, tests play an even more important role, but they also tend to be more lightweight. With all of these issues and more (e.g., asynchronous code), this book has you covered! ...