Part 1

Installation

Before we can start any coding, we need to make sure that your development environment has all the necessary applications installed and configured properly. I’m going to assume that you are using a recent Mac OSX installation.

First of all, you will need the CoffeeScript interpreter. The interpreter runs on top of node.js so you will need that, too.

This will give you two commands: node and coffee. The coffee command can be used to compile your CoffeeScript files into javascript. More on that later.

Homebrew

$ brew install node
$ brew install coffee-script

From source

$ git clone git://github.com/joyent/node.git
$ cd node/
$ ./configure
$ make
$ sudo make install
$ npm install -g coffee-script

Language primer

CoffeeScript is a little language that compiles into JavaScript. Underneath all those awkward braces and semicolons, JavaScript has always had a gorgeous object model at its heart. CoffeeScript is an attempt to expose the good parts of JavaScript in a simple way.

The golden rule of CoffeeScript is: “It’s just JavaScript”. The code compiles one-to-one into the equivalent JS, and there is no interpretation at runtime. You can use any existing JavaScript library seamlessly from CoffeeScript (and vice-versa). The compiled output is readable and pretty-printed, passes through JavaScript Lint without warnings, will work in every JavaScript implementation, and tends to run as fast or faster than the equivalent handwritten JavaScript.

Once you’ve used CoffeeScript or a while, you will not want to go back to plain JavaScript.

Variables

In JavaScript, all user-defined variables need to have the var keyword in front of it.

var name = 'John Smith';

In CoffeeScript, you can safely omit that.

name = 'John Smith'

Each variable is automatically scoped to the current closure. This prevents you from accidentally leaking the variable name into the outer scope.

Semicolons and whitespace

Instead of relying on semicolons to indicate the end of a statement, CoffeeScript uses significant whitespace. Much like Python, indentation is used to mark the body of a function or a for-loop.

files = ['photo.jpg', 'logo.png']

for file in files
  console.log file

Functions

Functions in CoffeeScript are composed of only a name and an arrow:

var greet = function() {
  console.log('Good morning');
};

greet = ->
  console.log 'Good morning'

And with an argument:

var greet = function(name) {
  console.log('Good morning, ' + name);
};

greet = (name) ->
  console.log 'Good morning, ' + name

Brackets

In simple situations, you can omit the () syntax.

console.log('hello');
alert('hello');
parseInt('1234', 10);

can be written as:

console.log 'hello'
alert 'hello'
parseInt '1234', 10

Objects can also be simplified:

var user = {
  first: 'John',
  last: 'Smith',
  age: 28
};

user =
  first: 'John'
  last: 'Smith'
  age: 28

Note the absence of commas, too.

Go to Part 2