Chapter 1: ES? Now & Future

Before you dive into this book, you should have a solid working proficiency over JavaScript up to the most recent standard (at the time of this writing), which is commonly called ES5 (technically ES 5.1). Here, we plan to talk squarely about the upcoming ES6, as well as cast our vision beyond to understand how JS will evolve moving forward.

If you are still looking for confidence with JavaScript, I highly recommend you read the other titles in this series first:

• Up & Going: Are you new to programming and JS? This is the roadmap you need to consult as you start your learning journey.
• Scope & Closures: Did you know that JS lexical scope is based on compiler (not interpreter!) semantics? Can you explain how closures are a direct result of lexical scope and functions as values?
• this & Object Prototypes: Can you recite the four simple rules for how this is bound? Have you been muddling through fake “classes” in JS instead of adopting the simpler “behavior delegation” design pattern? Ever heard of objects linked to other objects (OLOO)?
• Types & Grammar: Do you know the built-in types in JS, and more importantly, do you know how to properly and safely use coercion between types? How comfortable are you with the nuances of JS grammar/syntax?
• Async & Performance: Are you still using callbacks to manage your asynchrony? Can you explain what a promise is and why/how it solves “callback hell”? Do you know how to use generators to improve the legibility of async code? What exactly constitutes mature optimization of JS programs and individual operations?

If you’ve already read all those titles and you feel pretty comfortable with the topics they cover, it’s time we dive into the evolution of JS to explore all the changes coming not only soon but farther over the horizon.

Unlike ES5, ES6 is not just a modest set of new APIs added to the language. It incorporates a whole slew of new syntactic forms, some of which may take quite a bit of getting used to. There’s also a variety of new organization forms and new API helpers for various data types.

ES6 is a radical jump forward for the language. Even if you think you know JS in ES5, ES6 is full of new stuff you don’t know yet, so get ready! This book explores all the major themes of ES6 that you need to get up to speed on, and even gives you a glimpse of future features coming down the track that you should be aware of.

Warning: All code in this book assumes an ES6+ environment. At the time of this writing, ES6 support varies quite a bit in browsers and JS environments (like Node.js), so your mileage may vary.