test.coffee

class @Animal
  constructor: () ->
    @id = ""
 
  @urls: []

  @print: ->
    console.log @urls

  printInternal: ->
    console.log(@urls)


class @Dog extends @Animal
  @urls: ["aaa"]
class @Cat extends @Animal
  @urls: ["bbb"]
class @Rat extends @Animal

# this prints ["aaa"]
@Dog.print() 
# this prints ["bbb"]
@Cat.print()
# this prints an empty array
@Rat.print()

d = new @Dog()
# this doesn't print ["aaa"] :(
d.printInternal()