Never modify properties of object pointers on your prototype in javascript, or you break things higher up in the chain. I also show a good workaround

scary-thing.coffee

### BAD WAY ###

class Animal

Animal.prototype.foo = {bar: "baz"}

class Dog extends Animal

fred = new Dog()

fred.foo.bar = "broken"

alert(Animal.prototype.foo.bar)
# => "broken"



### WORKAROUND ###
class Animal

Animal.prototype.foo = {bar: "baz"}

class Dog extends Animal

fred = new Dog()

fred.foo = {}

fred.foo.bar = "broken"

alert(Animal.prototype.foo.bar)
# => "baz"