Class Variables

Problem

You want to create a class variable.

Solution

class Zoo
  @MAX_ANIMALS: 50
  MAX_ZOOKEEPERS: 3
  
  helpfulInfo: =>
    "Zoos may contain a maximum of #{@constructor.MAX_ANIMALS} animals"

Zoo.MAX_ANIMALS
# => 50

Zoo.MAX_ZOOKEEPERS
# => undefined (it is an instance variable)

zoo = new Zoo
zoo.MAX_ZOOKEEPERS
# => 3
zoo.helpfulInfo()
# => "Zoos may contain a maximum of 50 animals"

Discussion

Coffeescript will store these values on the object itself rather than on the object prototype (and thus on individual object instances), which conserves memory and gives a central location to store class-level values.