If you do web development, chances are you've at least heard of CoffeeScript. Though it's less than five years old, this little language has received a lot of attention, and it's getting harder to ignore. Maybe you've already worked with it a little bit, or maybe you're just wondering what the fuss is all about. Good news! CoffeeScript is a delightful language that can help you write better code and have fun doing it. In this book, we will explore the language itself, and find out first-hand how it can help us build beautiful web applications.
CoffeeScript is a programming language. Like most programming languages, it offers control structures to describe the logic of our application, simple data types to store and manipulate information, and functions to encapsulate sections of program execution.
What makes CoffeeScript special is the way it is compiled. When most languages are compiled, they are translated into machine code—low-level instructions to the computer's processor. CoffeeScript is different: when compiled, it is instead translated into JavaScript. We write CoffeeScript code, give it to the CoffeeScript compiler and receive JavaScript code as output. This output can then be passed to anything that consumes JavaScript, such as a browser, or a standalone JavaScript interpreter.
This technique, dubbed transcompilation, allows us to use an alternative language on platforms that only directly support JavaScript. Client-side web development is the most prominent example, since JavaScript is the only supported general-purpose scripting solution on most web browsers. Other platforms such as Node.js and Rhino also offer useful features, but expect JavaScript input. JavaScript is nothing if not prolific, and CoffeeScript allows us to make use of all that existing tooling, but to write our code in a different language.
CoffeeScript was certainly not the first (or last) language to target JavaScript platforms. Many established languages, such as Ruby, Python, C, and Java have one or more projects focused on compiling that language to JavaScript. And other languages have been developed specifically to target JavaScript—notably Dart, TypeScript, and Coco.
Note
The CoffeeScript wiki itself maintains an extensive list of other languages that compile to JavaScript. You can find it at https://github.com/jashkenas/coffee-script/wiki/List-of-languages-that-compile-to-JS.
While it's not alone in its approach, CoffeeScript has seen the most success of any language that compiles to JavaScript. It is the tenth most popular language on GitHub, it ships by default with Ruby on Rails, and it has large followings in both client-side and server-side developer communities.
So what makes CoffeeScript special? Just like Goldilocks and her pilfered porridge, CoffeeScript derives its strength from being just right. It is a marked improvement over JavaScript; we'll spend much of this book learning how CoffeeScript can help us write code that is more concise, easier to read, and less prone to bugs. However, CoffeeScript does not overreach on features. CoffeeScript has little to no runtime of its own—there is no extra metadata to track, no extra memory management, no non-standard data structures. Instead, CoffeeScript compiles directly to ordinary-looking JavaScript, much like what an experienced JavaScript developer might write. In fact, CoffeeScript is less a new language than it is a shorthand for easily expressing the best practices of JavaScript.
CoffeeScript is an eminently pragmatic language, and this is the secret to its success. It's easy for JavaScript developers to learn, and most expertise carries over. It doesn't incur performance penalties over plain JavaScript. CoffeeScript and JavaScript can coexist peacefully, so it's easy to introduce CoffeeScript into existing JavaScript projects. Perhaps most importantly, CoffeeScript avoids the "magic" that is so often a source of bugs when the developer's assumptions don't match the language designer's assumptions. With CoffeeScript, it's very easy to understand what the resulting JavaScript will do and how it will behave.
It might also help that CoffeeScript is fun.
Chapter 1, Running a CoffeeScript Program, will cover installing the CoffeeScript tools and running a simple CoffeeScript program in both the console and a web browser.
Chapter 2, Writing Your First Lines of CoffeeScript, will explore the syntax of CoffeeScript and how it compiles to JavaScript.
In Chapter 3, Building a Simple Application, we will build an interactive web application and learn a few more CoffeeScript features along the way.
Chapter 4, Improving Our Application, will add more features to our web application, and explore more powerful CoffeeScript syntax.
Chapter 5, Using Classes, will teach us all about classes in CoffeeScript. It will also cover how to use them, how they work, and how to integrate with popular JavaScript frameworks.
In Chapter 6, Refactoring with Classes, we will use the new skills from previous chapter to refactor our web application using class-based structures.
In Chapter 7, Advanced CoffeeScript Features, we will learn advanced CoffeeScript features and idioms that reduce errors and make our code easier to understand. We will use them to add more features to our web application.
Chapter 8, Going Asynchronous, will show how CoffeeScript can help us deal with asynchronous operations, and integrate a third-party JavaScript library into our CoffeeScript application.
In Chapter 9, Debugging, we will learn how to use source maps to track problems in our application all the way back to the CoffeeScript source.
Chapter 10, Using CoffeeScript in More Places, will cover how to integrate CoffeeScript compilation into several popular web application frameworks.
In Chapter 11, CoffeeScript on the Server, we will run CoffeeScript on the server with Node.js, and learn how to integrate it with standard JavaScript Node modules.
All you need for this book is a text editor and a working CoffeeScript compiler, and don't worry about the compiler—we'll cover installation and use of that tool in the first chapter! We provide instructions for using the tools on Windows, Mac OS X, and Linux. We'll be spending a lot of the book working on a client-side web application, so if you have any favorite development tools, feel free to bring those along. You'll also need a modern browser. The most recent version of Firefox or Chrome is ideal, but any other up-to-date browser such as Safari, Opera, or a recent Internet Explorer will also work fine.
Some familiarity with the JavaScript language will help—CoffeeScript is a close relative, so it's useful to understand what the compiler's output is doing. It's also helpful, though not necessary, to have some experience with client-side web development. We'll be building a web application with a lot of CoffeeScript, plus a little HTML and CSS.
No experience with CoffeeScript is necessary. We'll cater to everyone from the total newbie to the person who has hacked together some CoffeeScript already but wants a better grasp of what's going on and how to best utilize the language.
In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.
Code words in text are shown as follows: "We can pull in another module by using the require function."
A block of code is set as follows:
fibonacci = (n) ->
if n is 0 or n is 1
n
else
fibonacci(n-1) + fibonacci(n-2)When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
fibonacci = (n) ->
if n is 0 or n is 1
n
else
fibonacci(n-1) + fibonacci(n-2)
Any command-line input or output is written as follows:
coffee --compile --watch *.coffee
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "clicking the Next button moves you to the next screen".
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