1
Some JavaScript engines (Node, for example) do compile your JavaScript, but it happens transparently.
but it is going to put an extra burden on the programmer, as ES6 code has to be trans‐
compiled into “safe” ES5 to ensure that it can run anywhere.
Programmers who have been around a while might be thinking “big deal; back in my
day, there was no such thing as a language that didn’t have to be compiled and
linked!” I’ve been writing software long enough to remember that time, but I do not
miss it: I enjoy the lack of fuss in interpreted languages like JavaScript.
One of the advantages of JavaScript has always been its ubiquity: it became the stan‐
dard browser scripting language almost overnight, and with the advent of Node, its
use broadened beyond the browser. So it is a bit painful to recognize that it will prob‐
ably be a few years before you can ship ES6 code without worrying about browsers
that don’t support it. If you’re a Node developer, the situation is a little bit brighter:
because you only have one JavaScript engine to worry about, you can track the pro‐
gress of ES6 support in Node.
The ES6 examples in this book can be run in Firefox, or on a web‐
. For “real-world code,” however, you will
want to know the tools and techniques in this chapter.
One interesting aspect about JavaScript’s transition from ES5 to ES6 is that, unlike
language releases of the past, the adoption is gradual. That is, the browser you’re using
right now probably has some—but not all—features available in ES6. This gradual
transition is made possible in part by the dynamic nature of JavaScript, and in part by
the changing nature of browser updates. You may have heard the term evergreen used
to describe browsers: browser manufacturers are moving away from the concept of
having discrete browser versions that have to be updated. Browsers, they reason,
should be able to keep themselves up to date because they are always connected to the
Internet (at least if they are going to be useful). Browsers still have versions, but it is
now more reasonable to assume that your users have the latest version—because
evergreen browsers don’t give users the option not to upgrade.
Even with evergreen browsers, however, it will be a while before you can rely on all of
the great features of ES6 being available on the client side. So for the time being,
transcompilation (also called transpilation) is a fact of life.
ES6 Features
There are a lot of new features in ES6—so many that even the transcompilers we’ll be
talking about don’t currently support all of them. To help control the chaos, New
16 | Chapter 2: JavaScript Development Tools
