CoffeeScript is mad!

foo1.coffee

(->
  x = ->
    foo = false
  # If a variable is used after a function definition
  # for the first time...
  foo = true
)()

foo1.js

(function() {
  var foo, x;
  x = function() {
    // ... CoffeeScript adds a var keyword.
    var foo;
    return foo = false;
  };
  return foo = true;
})();

foo2.coffee

(->
  # If a variable is used before a function definition
  # for the first time...
  foo = true
  x = ->
    foo = false
)()

foo2.js

(function() {
  var foo, x;
  foo = true;
  return x = function() {
    // ... it doesn't add the var keyword
    return foo = false;
  };
})();