CoffeeScript 類方法和實例方法

類方法和實例方法

問題

你想創(chuàng)建類和實例的方法。

解決方案

類方法

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'

實例方法

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'

討論

Coffeescript會在對象本身中保存類方法（也叫靜態(tài)方法），而不是在對象原型中（以及單一的對象實例），在保存了記錄的同時也將類級的變量保存在中心位置。