wondering about this coffeescript thing

gistfile1.js

/*
 * Some quick hand-translations of code found in http://coffeescript.org/
 * I know they're trying to show off random features, but going through these
 * makes me wonder how much convenience CS actually adds.
 */

// # Assignment:
// number   = 42
// opposite = true
var number = 42;
var opposite = true;

// # Conditions:
// number = -42 if opposite
if (opposite) number = -42;

// # Functions:
// square = (x) -> x * x
var square = function(x) x*x; // Yes, this is legal.

// # Arrays:
// list = [1, 2, 3, 4, 5]
var list = [1, 2, 3, 4, 5];

// # Objects:
// math =
//   root:   Math.sqrt
//   square: square
//   cube:   (x) -> x * square x

var math = {
    root: Math.sqrt,
    square: square,
    cube: function(x) x * square(x)
};

// # Splats:
// race = (winner, runners...) ->
//   print winner, runners

// Splats are nice, but they don't save *that* much work...
var race = function(winner) {
    var runners = [].slice.call(arguments, 1);
    // or with lodash/underscore:
    // var runners = _.tail(arguments);
    console.log(winner, runners);
};


// # Existence:
// alert "I knew it!" if elvis?
if (elvis) alert("I knew it!");

// # Array comprehensions:
// cubes = (math.cube num for num in list)
var cubes = [math.cube(num) for (num of list)]; // JS 1.7
var cubes2 = list.map(math.cube); // Even better

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

function fill(container, liquid) {
    liquid = liquid || "coffee";
    return "Filling the "+container+" with "+liquid+"...";
};