类方法和实例方法

问题

创造类和实例的方法。

解决方案

类方法

class Songs
  @_titles: 0    # Although it's directly accessible, the leading _ defines it by convention as private property.

  @get_count: ->
    @_titles

  constructor: (@artist, @title) ->
    @constructor._titles++     # Refers to <Classname>._titles, in this case Songs.titles

Songs.get_count()
# => 0

song = new Songs("Rick Astley", "Never Gonna Give You Up")
Songs.get_count()
# => 1

song.get_count()
# => TypeError: Object <Songs> has no method 'get_count'

实例方法

class Songs
  _titles: 0    # Although it's directly accessible, the leading _ defines it by convention as private property.

  get_count: ->
    @_titles

  constructor: (@artist, @title) ->
    @_titles++

song = new Songs("Rick Astley", "Never Gonna Give You Up")
song.get_count()
# => 1

Songs.get_count()
# => TypeError: Object function Songs(artist, title) ... has no method 'get_count'

讨论

Coffeescript会在对象本身中中保存类方法（也叫静态方法），而不是在对象原型中（以及单一的对象实例），在保存了记录的同时也将类级的变量保存在中心位置。