• Compile a directory tree of .coffee files into a parallel tree of .js, in lib:

  coffee -o lib/ -c src/

• Watch a file for changes, and recompile it every time the file is saved:

  coffee --watch --compile experimental.coffee

• Concatenate a list of files into a single script:

  coffee --join project.js --compile src/*.coffee

• Print out the compiled JS from a one-liner:

  coffee -bpe "alert i for i in [0..10]"

• Start the CoffeeScript REPL:

  coffee

First, the basics: CoffeeScript uses significant whitespace to delimit blocks of code. You don't need to use semicolons ; to terminate expressions, ending the line will do just as well (although semicolons can still be used to fit multiple expressions onto a single line). Instead of using curly braces { } to surround blocks of code in functions, if-statements, switch, and try/catch, use indentation.

You don't need to use parentheses to invoke a function if you're passing arguments. The implicit call wraps forward to the end of the line or block expression.
console.log sys.inspect object → console.log(sys.inspect(object));

square = (x) -> x * x
cube   = (x) -> square(x) * x

fill = (container, liquid = "coffee") ->
  "Filling the #{container} with #{liquid}..."

song = ["do", "re", "mi", "fa", "so"]

singers = {Jagger: "Rock", Elvis: "Roll"}

bitlist = [
  1, 0, 1
  0, 0, 1
  1, 1, 0
]

kids =
  brother:
    name: "Max"
    age:  11
  sister:
    name: "Ida"
    age:  9

// when using reserved words
$('.account').attr class: 'active'
log object.class

The CoffeeScript compiler takes care to make sure that all of your variables are properly declared within lexical scope — you never need to write var yourself.

outer = 1
changeNumbers = ->
  inner = -1
  outer = 10
inner = changeNumbers()

If you'd like to create top-level variables for other scripts to use, attach them as properties on window, or on the exports object in CommonJS. The existential operator (covered below), gives you a reliable way to figure out where to add them; if you're targeting both CommonJS and the browser: exports ? this

mood = greatlyImproved if singing

if happy and knowsIt
  clapsHands()
  chaChaCha()
else
  showIt()

date = if friday then sue else jill

options or= defaults

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